feat: push product images to cloud for the QR menu

local_backend now uploads each product's image file to cloud_backend
during the existing ~5 min menu sync, so the QR menu can show real
photos without needing a manually-set digital_image_url. Only
re-uploads images whose content hash changed since the last push
(Product.cloud_image_hash), to avoid re-sending unchanged binaries
every cycle.

Also adds a manual "sync now" trigger (POST /api/system/sync-menu) and
a matching button in Settings → Operation, for pushing menu/price/image
changes immediately instead of waiting for the next automatic cycle.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

local_backend/routers/system.py

@@ -16,7 +16,7 @@ from models.user import User
 from models.product import Category, Product
 from models.table import Table, TableGroup
 from services import printer_service
-from services.cloud_sync import _sync_once
+from services.cloud_sync import _sync_once, _push_menu_snapshot
 from middleware.license_check import license_state
 from config import settings
 
@@ -106,6 +106,13 @@ async def sync_license_now(user: User = Depends(require_manager)):
     }
 
 
+@router.post("/sync-menu")
+async def sync_menu_now(user: User = Depends(require_manager)):
+    """Immediately push the digital menu snapshot (and any changed product images) to the cloud."""
+    await _push_menu_snapshot()
+    return {"ok": True}
+
+
 @router.get("/printers", response_model=List[PrinterOut])
 def list_printers(db: Session = Depends(get_db), user: User = Depends(require_manager)):
     return db.query(Printer).all()