fix: fix timezone handling across backend and frontend (v0.3.1)

- Add tz.py with local_strftime/to_local helpers that read system.timezone
  from DB and convert UTC datetimes to venue local time before formatting
- Fix all strftime() calls in orders.py, reports.py, printer_service.py
  that were formatting UTC datetimes without timezone conversion
- Fix get_order endpoint returning raw dicts without Z suffix on datetimes,
  causing JS new Date() to treat timestamps as local instead of UTC
- Fix fmtDate() in tokens.js that stripped the T separator before parsing,
  breaking UTC-to-local conversion for all report date displays
- Make open/partially_paid table chips more visually distinct on dashboard

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

manager_dashboard/src/pages/DashboardPage.jsx

@@ -65,8 +65,8 @@ function Avatar({ name, avatarUrl, size = 36 }) {
 // ─── Table color tokens ────────────────────────────────────────────────────────
 
 const TABLE_COLORS = {
-  open:           { bg: '#eef7f0', border: '#d7ecdc', dot: '#2f9e5e', text: '#1f7042', label: 'Ανοιχτό' },
-  partially_paid: { bg: '#f4eefb', border: '#e3d4f3', dot: '#7a44c9', text: '#57309a', label: 'Μερική πληρ.' },
+  open:           { bg: '#bbf7d0', border: '#4ade80', dot: '#16a34a', text: '#14532d', label: 'Ανοιχτό' },
+  partially_paid: { bg: '#e9d5ff', border: '#a855f7', dot: '#7c3aed', text: '#4c1d95', label: 'Μερική πληρ.' },
   free:           { bg: '#f4f4f2', border: '#dfe2e6', dot: '#8a9099', text: '#5a6169', label: 'Ελεύθερο' },
 }
 

manager_dashboard/src/ui/tokens.js

@@ -94,13 +94,9 @@ export const fmtTime = (iso) => {
 }
 export const fmtDate = (iso) => {
   if (!iso) return '—'
-  // Parse as local time by replacing the T separator so Date treats it as local
-  const d = new Date(String(iso).replace('T', ' '))
+  const d = new Date(iso)
   if (isNaN(d)) return String(iso)
-  const day = String(d.getDate()).padStart(2, '0')
-  const month = String(d.getMonth() + 1).padStart(2, '0')
-  const year = d.getFullYear()
-  return `${day}/${month}/${year}`
+  return d.toLocaleDateString('en-GB', { day: '2-digit', month: '2-digit', year: 'numeric' })
 }
 
 // Format a raw YYYY-MM-DD string (from a date picker) as DD/MM/YYYY without any timezone conversion