feat: refresh a single repository from its own button (#2)

* feat(refresh): refresh a single repository with POST /refresh?repo=

The endpoint refreshes one configured repository and returns the full state plus the repo name.
Each repository has a 60-second cooldown that is separate from the full-refresh limit.
A running full refresh or a refresh of the same repository returns 409.
An unknown repository returns 404. Cross-site and disabled-config behaviour stay the same.
The collector reuses its fetch path and replaces only that repository.

* feat(ui): add a refresh button beside each repository

The button appears in the project list and in each attention group header.
It stays hidden when the server disables manual refresh.
The button shows a spinner while its repository refreshes and reports refusals in the notice line.
The store swaps in the returned state, so no extra fetch follows.

src/lib/types.ts

@@ -56,6 +56,9 @@ export interface TrackerState {
   alerts: Alert[]
 }
 
+/** Answer to a single-repository refresh: the state after it, plus the repo name. */
+export type RepoRefreshResult = TrackerState & { repo: string }
+
 /** One line in a repo block: every alert that targets the same URL, merged. */
 export interface Row {
   kind: string