Add 'use main stack settings' toggle for third-party integration credentials

Each of Newbook, Resos, SambaPOS, SMTP, and Nextcloud now has a checkbox at the
top of its credentials block. When enabled, the app reads auth credentials from
the central stack settings service (SETTINGS_URL + STACK_INTERNAL_SECRET) and
the local auth fields are grayed out. App-specific fields (base path, GL codes,
keywords, sync intervals, etc.) remain editable regardless.

Backend: new use_global_* columns on kitchen_settings, migration, global_settings_service
with apply_global_overrides() for in-memory credential injection, GET /api/settings/global-status
endpoint, and apply_global_overrides() called in test-connection endpoints and FileArchivalService.

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

backend/api/settings.py

@@ -49,6 +49,8 @@ class SettingsResponse(BaseModel):
     llm_confidence_threshold: float | None = None
     llm_monthly_token_limit: int = 500000
     llm_features_enabled: dict | None = None
+    # Global stack settings delegation
+    use_global_smtp: bool = False
 
     class Config:
         from_attributes = True
@@ -92,6 +94,8 @@ class SettingsUpdate(BaseModel):
     llm_confidence_threshold: float | None = None
     llm_monthly_token_limit: int | None = None
     llm_features_enabled: dict | None = None
+    # Global stack settings delegation
+    use_global_smtp: bool | None = None
 
 
 @router.get("/", response_model=SettingsResponse)
@@ -158,6 +162,7 @@ def _build_settings_response(settings: KitchenSettings) -> SettingsResponse:
         llm_confidence_threshold=float(settings.llm_confidence_threshold) if settings.llm_confidence_threshold else None,
         llm_monthly_token_limit=settings.llm_monthly_token_limit,
         llm_features_enabled=settings.llm_features_enabled,
+        use_global_smtp=settings.use_global_smtp,
     )
 
 
@@ -237,7 +242,13 @@ async def test_smtp_connection(
     )
     settings = result.scalar_one_or_none()
 
-    if not settings or not settings.smtp_host or not settings.smtp_from_email:
+    if not settings:
+        raise HTTPException(status_code=400, detail="SMTP not configured")
+
+    from services.global_settings_service import apply_global_overrides
+    await apply_global_overrides(settings)
+
+    if not settings.smtp_host or not settings.smtp_from_email:
         raise HTTPException(
             status_code=400,
             detail="SMTP not fully configured. Please set SMTP host and from email."
@@ -404,6 +415,7 @@ class NextcloudSettingsResponse(BaseModel):
     nextcloud_base_path: str | None
     nextcloud_enabled: bool
     nextcloud_delete_local: bool
+    use_global_nextcloud: bool = False
 
     class Config:
         from_attributes = True
@@ -416,6 +428,7 @@ class NextcloudSettingsUpdate(BaseModel):
     nextcloud_base_path: str | None = None
     nextcloud_enabled: bool | None = None
     nextcloud_delete_local: bool | None = None
+    use_global_nextcloud: bool | None = None
 
 
 class NextcloudStatsResponse(BaseModel):
@@ -450,7 +463,8 @@ async def get_nextcloud_settings(
             nextcloud_password_set=False,
             nextcloud_base_path="/Kitchen Invoices",
             nextcloud_enabled=False,
-            nextcloud_delete_local=False
+            nextcloud_delete_local=False,
+            use_global_nextcloud=False,
         )
 
     return NextcloudSettingsResponse(
@@ -459,7 +473,8 @@ async def get_nextcloud_settings(
         nextcloud_password_set=bool(settings.nextcloud_password),
         nextcloud_base_path=settings.nextcloud_base_path,
         nextcloud_enabled=settings.nextcloud_enabled,
-        nextcloud_delete_local=settings.nextcloud_delete_local
+        nextcloud_delete_local=settings.nextcloud_delete_local,
+        use_global_nextcloud=settings.use_global_nextcloud,
     )
 
 
@@ -499,10 +514,20 @@ async def update_nextcloud_settings(
         nextcloud_password_set=bool(settings.nextcloud_password),
         nextcloud_base_path=settings.nextcloud_base_path,
         nextcloud_enabled=settings.nextcloud_enabled,
-        nextcloud_delete_local=settings.nextcloud_delete_local
+        nextcloud_delete_local=settings.nextcloud_delete_local,
+        use_global_nextcloud=settings.use_global_nextcloud,
     )
 
 
+@router.get("/global-status")
+async def get_global_status(
+    current_user: User = Depends(get_current_user),
+):
+    """Check which integrations are configured in the central stack settings service."""
+    from services.global_settings_service import check_global_status
+    return await check_global_status()
+
+
 @router.post("/nextcloud/test")
 async def test_nextcloud_connection(
     current_user: User = Depends(get_current_user),
@@ -516,7 +541,13 @@ async def test_nextcloud_connection(
     )
     settings = result.scalar_one_or_none()
 
-    if not settings or not all([settings.nextcloud_host, settings.nextcloud_username, settings.nextcloud_password]):
+    if not settings:
+        raise HTTPException(status_code=400, detail="Nextcloud not fully configured")
+
+    from services.global_settings_service import apply_global_overrides
+    await apply_global_overrides(settings)
+
+    if not all([settings.nextcloud_host, settings.nextcloud_username, settings.nextcloud_password]):
         raise HTTPException(status_code=400, detail="Nextcloud not fully configured")
 
     nc = NextcloudService(