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/services/global_settings_service.py

@@ -43,6 +43,7 @@ async def check_global_status() -> dict[str, bool]:
         "newbook": ["api_key"],
         "resos": ["api_key"],
         "sambapos": ["password"],
+        "azure": ["api_key"],
     }
     results: dict[str, bool] = {}
     for slug, fields in required.items():
@@ -95,3 +96,9 @@ async def apply_global_overrides(settings) -> None:
             settings.sambapos_db_name = creds.get("database") or settings.sambapos_db_name
             settings.sambapos_db_username = creds.get("username") or settings.sambapos_db_username
             settings.sambapos_db_password = creds.get("password") or settings.sambapos_db_password
+
+    if getattr(settings, "use_global_azure", False):
+        creds = await get_global_integration("azure")
+        if creds:
+            settings.azure_endpoint = creds.get("endpoint") or settings.azure_endpoint
+            settings.azure_key = creds.get("api_key") or settings.azure_key