feat: Phase 2F — customer CRM

Backend:
- New model: Customer (customers table) — name, nickname, phone, email, notes, is_active
- Order model: add customer_id nullable FK → customers
- New router: /api/customers/ — list (with ?search=), create, get, update, soft-delete,
  GET /{id}/orders (visit history with totals)
- Each CustomerOut includes visit_count + total_spent (computed from closed/paid orders)
- PUT /api/orders/{id}/customer — assign or unassign a customer; manager-only;
  validates customer is active; broadcasts order_updated SSE event
- GET /api/orders/{id} now returns customer_id, customer_name (with nickname), customer_phone
- Migration: CREATE TABLE customers + ALTER TABLE orders ADD COLUMN customer_id

Frontend:
- CustomersPage (/customers): searchable list (name/nickname/phone), avatar initials,
  visit count + total_spent on each row; click → detail panel slides in showing stats
  (visits, total spent, avg ticket), contact info, notes, full visit history
- OrderDetailPage: new Πελάτης card — shows assigned customer in blue if set;
  for open orders shows "+ Ανάθεση πελάτη" button → inline search dropdown → assign;
  Αφαίρεση button to unassign
- Sidebar: Users icon for Πελάτες (between Επαφές and Ρυθμίσεις)

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

local_backend/main.py

@@ -22,6 +22,7 @@ import models.message       # noqa: F401 — registers StaffMessage, StaffMessag
 import models.reservation   # noqa: F401
 import models.notes          # noqa: F401 — registers SiteNote, SiteTodo
 import models.expenses       # noqa: F401 — registers Contact, Expense, ExpensePayment
+import models.customers      # noqa: F401 — registers Customer
 
 from routers import auth, tables, products, orders, waiters, reports, system, setup as setup_router
 from routers import business_day as business_day_router
@@ -35,6 +36,7 @@ from routers import connect_orders as connect_orders_router
 from routers import reservations as reservations_router
 from routers import notes as notes_router
 from routers.expenses import contacts_router, expenses_router
+from routers import customers as customers_router
 
 
 def _run_migrations():
@@ -273,6 +275,19 @@ def _run_migrations():
         # Phase 2B — staff payroll
         "ALTER TABLE users ADD COLUMN hourly_rate REAL",
         "ALTER TABLE waiter_shifts ADD COLUMN hourly_rate_snapshot REAL",
+        # Phase 2F — customer CRM
+        """CREATE TABLE IF NOT EXISTS customers (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            name VARCHAR NOT NULL,
+            nickname VARCHAR,
+            phone VARCHAR,
+            email VARCHAR,
+            notes TEXT,
+            is_active INTEGER NOT NULL DEFAULT 1,
+            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+            created_by_id INTEGER NOT NULL REFERENCES users(id)
+        )""",
+        "ALTER TABLE orders ADD COLUMN customer_id INTEGER REFERENCES customers(id)",
         # Phase 2E — cash drawer reconciliation
         "ALTER TABLE waiter_shifts ADD COLUMN counted_cash_end REAL",
         "ALTER TABLE waiter_shifts ADD COLUMN cash_discrepancy REAL",
@@ -396,3 +411,4 @@ app.include_router(reservations_router.router,   prefix="/api/reservations", tag
 app.include_router(notes_router.router,          prefix="/api/notes",        tags=["notes"])
 app.include_router(contacts_router,              prefix="/api/contacts",     tags=["contacts"])
 app.include_router(expenses_router,              prefix="/api/expenses",     tags=["expenses"])
+app.include_router(customers_router.router,      prefix="/api/customers",    tags=["customers"])