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.

frontend/src/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: frontend/src
 
 ## role
-Frontend application entry point and core infrastructure providing routing, OIDC authentication, global state, and styling for a React-based admin dashboard.
+Frontend React application providing an admin dashboard UI with OIDC authentication, dark mode, and user activity management for a Jellyfin media server.
 ## parent
 index: frontend/.pi-map.index.md
 map: frontend/.pi-map.md