Make service connection config editable on service page

The service detail page showed non-secret connection config (base_url,
user_id, username, timeout_seconds) as read-only. Render schema-driven
editable inputs (reusing the create-dialog pattern) with a draftConfig
state hydrated from the instance, and unify the save button to persist
both config and secrets. Number fields render as type=number; the base_url
schema description surfaces as helper text.

backend/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: backend
 
 ## role
-FastAPI backend service providing JWT-protected REST APIs for Jellyfin media browsing, SSH file inspection, and server monitoring.
+FastAPI backend service providing Jellyfin media browsing, SSH file inspection, server monitoring, and JWT-protected API endpoints.
 ## parent
 index: ./.pi-map.index.md
 map: ./.pi-map.md