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/tests/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: backend/tests
 
 ## role
-Test suite providing unit and integration coverage for the backend's API endpoints, clients, configuration, utilities, and services.
+Test suite providing unit and integration tests that validate API endpoints, configuration, external clients, utilities, and service logic across the backend.
 ## parent
 index: backend/.pi-map.index.md
 map: backend/.pi-map.md