Dedup _resolve_service_record into shared service_resolution module

Extract the duplicated _resolve_service_record helper (identical in
routers/monitoring.py and routers/authentik_users.py) into a shared
services/service_resolution.py module. Both routers now import
resolve_service_record from the shared module.

The authentik router previously hardcoded service_type='authentik' in
its local copy; the shared helper takes service_type as a param (same
as monitoring's did).

Tests updated: test_api.py patches now target the correct module paths
(resolve_service_record on the monitoring module where it's imported,
build_service_record on the service_resolution module).

283 backend tests pass; ruff clean.

backend/src/media_library_viewer_api/routers/monitoring.py

@@ -15,34 +15,14 @@ import requests
 from fastapi import APIRouter, Body, Depends
 
 from media_library_viewer_api.dependencies import get_settings_store
+from media_library_viewer_api.services.service_resolution import resolve_service_record
 from media_library_viewer_api.services.settings_store import SettingsStore
 from media_library_viewer_api.services.targets import build_node_exporter_targets
-from media_library_viewer_api.widgets.sources import ServiceRecord, build_service_record
+from media_library_viewer_api.widgets.sources import ServiceRecord
 
 logger = logging.getLogger(__name__)
 
 
-def _resolve_service_record(
-    store: SettingsStore, service_type: str, service_id: str | None = None
-) -> ServiceRecord | None:
-    """Return the requested service instance, else the first enabled one.
-
-    Returns ``None`` when the instance does not exist / is the wrong type, or
-    when no enabled instance of ``service_type`` is configured.
-    """
-    if service_id:
-        row = store.get_service(service_id)
-        if not row or row.get("service_type") != service_type:
-            return None
-        if not row.get("enabled", True):
-            return None
-        return build_service_record(store, row)
-    for row in store.list_services(service_type):
-        if row.get("enabled", True):
-            return build_service_record(store, row)
-    return None
-
-
 def _base_url(service: ServiceRecord) -> str:
     return str(service.config.get("base_url") or "").rstrip("/")
 
@@ -104,7 +84,7 @@ def get_alertmanager_alerts(
     is configured the endpoint returns an empty summary with an
     ``alertmanager_not_configured`` error so the UI can render a health card.
     """
-    service = _resolve_service_record(store, "alertmanager", service_id)
+    service = resolve_service_record(store, "alertmanager", service_id)
     if service is None:
         return {"total": 0, "by_severity": {}, "alerts": [], "error": "alertmanager_not_configured"}
     try:
@@ -149,7 +129,7 @@ def get_alertmanager_status(
     store: SettingsStore = Depends(get_settings_store),
 ) -> dict[str, Any]:
     """Return Alertmanager cluster/status for the UI health card."""
-    service = _resolve_service_record(store, "alertmanager", service_id)
+    service = resolve_service_record(store, "alertmanager", service_id)
     if service is None:
         return {
             "up": False,
@@ -198,7 +178,7 @@ def get_grafana_status(
     store: SettingsStore = Depends(get_settings_store),
 ) -> dict[str, Any]:
     """Probe a Grafana service instance's ``/api/health`` endpoint."""
-    service = _resolve_service_record(store, "grafana", service_id)
+    service = resolve_service_record(store, "grafana", service_id)
     if service is None:
         return _status_response(None, error="no_service_configured")
     try:
@@ -221,7 +201,7 @@ def get_prometheus_status(
     store: SettingsStore = Depends(get_settings_store),
 ) -> dict[str, Any]:
     """Probe a Prometheus service instance's health and build info."""
-    service = _resolve_service_record(store, "prometheus", service_id)
+    service = resolve_service_record(store, "prometheus", service_id)
     if service is None:
         return _status_response(None, error="no_service_configured")
     base = _base_url(service)