Wire Azure OCR to central settings toggle; remove redundant Users section

- settings/src/integrations/schema.js: rename azure from 'Azure AD' to
  'Azure Document Intelligence', swap fields to endpoint + api_key
- Add use_global_azure column (migration + model)
- global_settings_service: add azure to check_global_status and apply_global_overrides
- api/settings.py: expose use_global_azure in response/update; apply overrides
  in test_azure_connection before credential check
- Settings.tsx: add 'Use credentials from main stack settings' toggle for
  Azure OCR section (endpoint/key disabled when on, test button enabled when
  global is configured); remove Users section (managed centrally via auth
  service), clean up UserData interface, users query and mutations

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

backend/migrations/add_global_settings_flags.py

@@ -12,6 +12,7 @@ async def migrate():
             "ALTER TABLE kitchen_settings ADD COLUMN IF NOT EXISTS use_global_newbook BOOLEAN DEFAULT FALSE",
             "ALTER TABLE kitchen_settings ADD COLUMN IF NOT EXISTS use_global_resos BOOLEAN DEFAULT FALSE",
             "ALTER TABLE kitchen_settings ADD COLUMN IF NOT EXISTS use_global_sambapos BOOLEAN DEFAULT FALSE",
+            "ALTER TABLE kitchen_settings ADD COLUMN IF NOT EXISTS use_global_azure BOOLEAN DEFAULT FALSE",
         ]:
             try:
                 await conn.execute(text(col))