feat: Phase 2L — discount audit report

Backend:
- GET /api/reports/discounts: read-only audit of all OrderDiscount records
  Filters: ?from=&to= or ?business_day_id=, ?applied_by=
  Returns:
  - discounts[]: id, order_id, table_name, applied_by_name, applied_at, discount_type,
    discount_value, discount_amount (computed euro value), order_total_before,
    item_id (null = whole-order), reason
  - total_discount_value: sum of all euro discount amounts
  - order_count: unique orders that received a discount
  - by_waiter[]: grouped summary (waiter_name, count, total_value)
  discount_amount computation: fixed → discount_value directly;
    percent → computed from order or item total at query time

Frontend:
- DiscountsLog.jsx: read-only report under Reports → Λειτουργίες → Εκπτώσεις
  - Filter bar: range/workday toggle, date range, waiter filter
  - 3 stat cards: total discount value, orders with discounts, count of entries
  - By-waiter summary table (hidden when only one waiter)
  - Full audit table: date, order + table, waiter, type badge (% blue / € amber),
    order total before, euro amount discounted in amber, reason
  - Totals footer row
  - No create/edit/delete — pure audit log

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

manager_dashboard/src/pages/reports/ReportsPage.jsx

@@ -22,6 +22,7 @@ import TableAnalytics from './restaurant/TableAnalytics'
 import PrinterHistory from './operations/PrinterHistory'
 import PrinterHealthLog from './operations/PrinterHealthLog'
 import CancellationsLog from './operations/CancellationsLog'
+import DiscountsLog from './operations/DiscountsLog'
 
 const PARENT_TABS = [
   {
@@ -58,6 +59,7 @@ const PARENT_TABS = [
       { id: 'printer-history', label: 'Ιστορικό Εκτυπωτή',  Component: PrinterHistory },
       { id: 'printer-health',  label: 'Υγεία Εκτυπωτή',     Component: PrinterHealthLog },
       { id: 'cancellations',   label: 'Ακυρώσεις',           Component: CancellationsLog },
+      { id: 'discounts',       label: 'Εκπτώσεις',           Component: DiscountsLog },
     ],
   },
 ]

manager_dashboard/src/pages/reports/operations/DiscountsLog.jsx

@@ -0,0 +1,191 @@
+import { useState } from 'react'
+import { useQuery } from '@tanstack/react-query'
+import { Tag } from 'lucide-react'
+import client from '../../../api/client'
+import { FilterBar, FilterSelect, FilterDateInput, WorkDayDateToggle } from '../shared/FilterBar'
+import { Panel, DataTable, THead, TH, TR, TD, WaiterAvatar } from '../shared/TablePrimitives'
+import StatCard from '../shared/StatCard'
+import EmptyState from '../shared/EmptyState'
+import SkeletonTable from '../shared/SkeletonTable'
+import { fmtEUR, fmtNum, fmtDate, fmtTime, fmtDateTime, fmtDateStr } from '../shared/reportDesignTokens'
+
+function today() { return new Date().toISOString().slice(0, 10) }
+function monthAgo() { const d = new Date(); d.setDate(d.getDate() - 30); return d.toISOString().slice(0, 10) }
+
+export default function DiscountsLog() {
+  const [mode, setMode] = useState('range')
+  const [from, setFrom] = useState(monthAgo())
+  const [to, setTo] = useState(today())
+  const [businessDayId, setBusinessDayId] = useState('all')
+  const [waiterF, setWaiterF] = useState('all')
+
+  const { data: waitersData } = useQuery({
+    queryKey: ['meta-waiters'],
+    queryFn: () => client.get('/api/reports/meta/waiters').then(r => r.data),
+    staleTime: 5 * 60 * 1000,
+  })
+  const { data: bdData } = useQuery({
+    queryKey: ['business-days-list'],
+    queryFn: () => client.get('/api/reports/business-days').then(r => r.data),
+    staleTime: 60 * 1000,
+  })
+
+  const queryParams = {
+    ...(mode === 'workday' && businessDayId !== 'all' ? { business_day_id: businessDayId } : {}),
+    ...(mode === 'range' ? { from: from + 'T00:00:00', to: to + 'T23:59:59' } : {}),
+    ...(waiterF !== 'all' ? { applied_by: waiterF } : {}),
+  }
+
+  const { data, isLoading, isError, refetch } = useQuery({
+    queryKey: ['discounts', mode, from, to, businessDayId, waiterF],
+    queryFn: () => client.get('/api/reports/discounts', { params: queryParams }).then(r => r.data),
+    staleTime: 60 * 1000,
+  })
+
+  const waiterOptions = [
+    { value: 'all', label: 'Όλοι' },
+    ...((waitersData?.waiters || []).map(w => ({ value: String(w.id), label: w.name }))),
+  ]
+  const bdOptions = [
+    { value: 'all', label: 'Όλες οι Εργάσιμες Μέρες' },
+    ...((bdData?.business_days || []).map(bd => ({ value: String(bd.id), label: `${fmtDate(bd.opened_at)} · ${fmtTime(bd.opened_at)}` }))),
+  ]
+
+  const discounts = data?.discounts || []
+  const byWaiter = data?.by_waiter || []
+  const totalValue = data?.total_discount_value ?? 0
+  const orderCount = data?.order_count ?? 0
+
+  if (isLoading) return <div className="flex-1 overflow-y-auto p-6"><SkeletonTable rows={8} columns={7} /></div>
+  if (isError) return (
+    <div className="flex flex-col flex-1 min-h-0">
+      <FilterBar><span className="text-[12px] text-slate-500">Αδυναμία φόρτωσης δεδομένων</span></FilterBar>
+      <div className="flex flex-1 items-center justify-center">
+        <button onClick={() => refetch()} className="rounded-md border border-slate-200 px-4 py-2 text-sm hover:bg-slate-50">Επανάληψη</button>
+      </div>
+    </div>
+  )
+
+  return (
+    <div className="flex flex-col flex-1 min-h-0">
+      <FilterBar>
+        <WorkDayDateToggle mode={mode} onChange={setMode} />
+        {mode === 'workday' ? (
+          <FilterSelect value={businessDayId} onChange={setBusinessDayId} options={bdOptions} width="w-72" label="Μέρα" />
+        ) : (
+          <>
+            <FilterDateInput value={from} onChange={setFrom} label="Από" />
+            <FilterDateInput value={to} onChange={setTo} label="Έως" />
+          </>
+        )}
+        <FilterSelect value={waiterF} onChange={setWaiterF} options={waiterOptions} label="Σερβιτόρος" />
+      </FilterBar>
+
+      <div className="flex-1 overflow-y-auto p-6 space-y-4">
+        {/* Summary cards */}
+        <div className="grid grid-cols-3 gap-4">
+          <StatCard label="Σύνολο Εκπτώσεων" value={fmtEUR(totalValue)} icon={Tag} color="amber" />
+          <StatCard label="Παραγγελίες με Έκπτωση" value={fmtNum(orderCount)} color="slate" />
+          <StatCard label="Αριθμός Εκπτώσεων" value={fmtNum(discounts.length)} color="slate" />
+        </div>
+
+        {/* By waiter summary */}
+        {byWaiter.length > 1 && (
+          <Panel title="Ανά Σερβιτόρο" padded={false}>
+            <DataTable>
+              <THead>
+                <TH>Σερβιτόρος</TH>
+                <TH align="right">Αριθμός</TH>
+                <TH align="right">Σύνολο</TH>
+                <TH align="right">Μέσος / Έκπτωση</TH>
+              </THead>
+              <tbody>
+                {byWaiter.map(w => (
+                  <TR key={w.waiter_id} striped>
+                    <TD><WaiterAvatar name={w.waiter_name} id={w.waiter_id} /></TD>
+                    <TD mono align="right">{fmtNum(w.count)}</TD>
+                    <TD mono align="right" className="font-semibold text-amber-700">{fmtEUR(w.total_value)}</TD>
+                    <TD mono align="right">{fmtEUR(w.count > 0 ? w.total_value / w.count : 0)}</TD>
+                  </TR>
+                ))}
+              </tbody>
+            </DataTable>
+          </Panel>
+        )}
+
+        {/* Full log */}
+        <Panel
+          title="Αρχείο Εκπτώσεων"
+          subtitle={`${discounts.length} εγγραφές — μόνο ανάγνωση`}
+          padded={false}
+        >
+          {discounts.length === 0 ? (
+            <EmptyState
+              icon={Tag}
+              title="Δεν βρέθηκαν εκπτώσεις"
+              description="Δεν υπάρχουν εκπτώσεις για την επιλεγμένη περίοδο."
+            />
+          ) : (
+            <DataTable>
+              <THead>
+                <TH>Ημ/νία</TH>
+                <TH>Παραγγελία</TH>
+                <TH>Σερβιτόρος</TH>
+                <TH align="right">Τύπος</TH>
+                <TH align="right">Τιμή πριν</TH>
+                <TH align="right">Ποσό Έκπτωσης</TH>
+                <TH>Αιτία</TH>
+              </THead>
+              <tbody>
+                {discounts.map(d => {
+                  const typeLabel = d.discount_type === 'percent'
+                    ? `${d.discount_value}%`
+                    : fmtEUR(d.discount_value)
+                  const isItemLevel = d.item_id != null
+                  return (
+                    <TR key={d.id} striped>
+                      <TD mono className="text-slate-500">{fmtDateTime(d.applied_at)}</TD>
+                      <TD>
+                        <span className="font-medium text-slate-900">
+                          #{d.order_id}
+                          {d.table_name && <span className="text-slate-400 font-normal ml-1">· {d.table_name}</span>}
+                        </span>
+                        {isItemLevel && (
+                          <span className="ml-2 text-[10px] font-semibold px-1.5 py-0.5 rounded bg-slate-100 text-slate-500">ΑΝΤΙΚ.</span>
+                        )}
+                      </TD>
+                      <TD><WaiterAvatar name={d.applied_by_name} id={d.applied_by_id} /></TD>
+                      <TD mono align="right">
+                        <span className={`text-xs font-semibold px-1.5 py-0.5 rounded ${d.discount_type === 'percent' ? 'bg-blue-50 text-blue-700' : 'bg-amber-50 text-amber-700'}`}>
+                          {typeLabel}
+                        </span>
+                      </TD>
+                      <TD mono align="right" className="text-slate-500">
+                        {d.order_total_before != null ? fmtEUR(d.order_total_before) : '—'}
+                      </TD>
+                      <TD mono align="right" className="font-semibold text-amber-700">
+                        − {fmtEUR(d.discount_amount)}
+                      </TD>
+                      <TD className="text-slate-500 text-[12px]">
+                        {d.reason || <span className="text-slate-300">—</span>}
+                      </TD>
+                    </TR>
+                  )
+                })}
+              </tbody>
+              {discounts.length > 1 && (
+                <tfoot>
+                  <TR>
+                    <TD colSpan={5} className="font-semibold text-slate-700">Σύνολο</TD>
+                    <TD mono align="right" className="font-bold text-amber-700">− {fmtEUR(totalValue)}</TD>
+                    <TD />
+                  </TR>
+                </tfoot>
+              )}
+            </DataTable>
+          )}
+        </Panel>
+      </div>
+    </div>
+  )
+}