fix: QR menu branding fields — display name, header image, empty-to-hide

- menu_display_name is now separate from the site's internal name (was
  incorrectly showing the sysadmin-only site name on the public menu).
- Header image now resolves against the cloud API origin instead of
  the menu-app's own origin, fixing the broken-image icon.
- Tagline/blurb/hours now genuinely hide when cleared: the sysadmin
  save handler was converting empty fields to null, which the PUT
  endpoint's exclude_none silently drops instead of clearing.
- Added a settable blurb (EN/GR) below the tagline, previously
  hardcoded ("Fresh seasonal plates, served with care.").
- Collapsed hours from two fields (EN/GR) to one — opening hours don't
  vary by language.

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

cloud_backend/main.py

@@ -45,9 +45,13 @@ def _run_migrations():
         "ALTER TABLE sites ADD COLUMN menu_mode VARCHAR NOT NULL DEFAULT 'order'",
         "ALTER TABLE sites ADD COLUMN menu_tagline_en VARCHAR",
         "ALTER TABLE sites ADD COLUMN menu_tagline_gr VARCHAR",
-        "ALTER TABLE sites ADD COLUMN menu_hours_en VARCHAR",
-        "ALTER TABLE sites ADD COLUMN menu_hours_gr VARCHAR",
+        "ALTER TABLE sites ADD COLUMN menu_hours_en VARCHAR",  # superseded by menu_hours, kept for history
+        "ALTER TABLE sites ADD COLUMN menu_hours_gr VARCHAR",  # superseded by menu_hours, kept for history
         "ALTER TABLE sites ADD COLUMN menu_header_image_url VARCHAR",
+        "ALTER TABLE sites ADD COLUMN menu_display_name VARCHAR",
+        "ALTER TABLE sites ADD COLUMN menu_blurb_en VARCHAR",
+        "ALTER TABLE sites ADD COLUMN menu_blurb_gr VARCHAR",
+        "ALTER TABLE sites ADD COLUMN menu_hours VARCHAR",
     ]
     for sql in migrations:
         try: