feat(connect): Phase 2 — cloud DB models for Xenia Connect

Adds three new tables created automatically by create_all on next
startup, plus an additive migration for an existing table:

models/menu_snapshot.py (NEW)
  - menu_snapshots: one row per site, holds the full serialized
    category+product JSON; upserted on each sync from local_backend

models/online_order.py (NEW)
  - online_orders: full order lifecycle from customer submission
    through delivery; tracks sync state so local_backend can poll
    for unprocessed orders (synced_to_local=0)

models/manager_account.py (NEW)
  - manager_accounts + manager_site_access (M2M join table): remote
    manager login accounts with per-site access control

models/site.py (MODIFIED)
  - order_counter column added; incremented atomically when each
    online order is created to generate "ORD-XXXX" public_ref values

main.py (MODIFIED)
  - imports all three new models so create_all registers their tables
  - _run_migrations() added (same pattern as local_backend) for the
    additive order_counter column on the existing sites table

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

cloud_backend/main.py

@@ -5,8 +5,11 @@ from fastapi.middleware.cors import CORSMiddleware
 from config import settings
 from database import engine, Base
 from auth_utils import hash_password
-import models.admin  # noqa: F401
-import models.site   # noqa: F401
+import models.admin           # noqa: F401
+import models.site            # noqa: F401
+import models.menu_snapshot   # noqa: F401
+import models.online_order    # noqa: F401
+import models.manager_account # noqa: F401
 
 from routers import auth, sites, heartbeat
 
@@ -25,9 +28,26 @@ def _seed_default_admin():
             db.commit()
 
 
+def _run_migrations():
+    """Apply additive schema changes that create_all won't handle."""
+    from sqlalchemy import text
+    migrations = [
+        # Per-site order counter for public_ref generation (e.g. "ORD-0042")
+        "ALTER TABLE sites ADD COLUMN order_counter INTEGER NOT NULL DEFAULT 0",
+    ]
+    for sql in migrations:
+        try:
+            with engine.connect() as conn:
+                conn.execute(text(sql))
+                conn.commit()
+        except Exception:
+            pass
+
+
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     Base.metadata.create_all(bind=engine)
+    _run_migrations()
     _seed_default_admin()
     yield