fix(subs): stop the lock/reload on source actions + regroup the row buttons

Lock/reload: every inline source action (check / backfill / recover / toggle /
remove) ended by refetching the WHOLE subscription list (store.loadAll /
refresh), which blocked the UI and re-rendered the table — collapsing the
expanded row, which read as "locks then resets." The action APIs already return
the updated source, so the store now patches that one row in place
(_patchSource / _dropSource); the post-action loadAll/refresh calls are gone.
Toggling enabled, starting/stopping a backfill, recovering, and removing are now
instant and leave the expansion intact.

Button regroup (operator-flagged: tiny, mis-clickable, not grouped by function):
- New shared SourceActions.vue used by desktop SourceRow + mobile SourceCard.
- Frequent actions stay as size="small" buttons: Check, Backfill/Stop.
- Low-frequency / destructive actions move into a labelled overflow (⋮) menu —
  Preview backfill, Recover dropped near-duplicates, Remove source — so they
  can't be fat-fingered, and the labels spell out recover-vs-backfill.
- Edit moves next to the source URL (its identity), out of the action cluster
  where it sat beside Remove.
- Single-source Remove now confirms (it had no guard before).

Tests: store patches/drops in place without dropping the cache.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/stores/sources.js

@@ -32,6 +32,31 @@ export const useSourcesStore = defineStore('sources', () => {
     if (artistId != null) byArtist.value.delete(artistId)
   }
 
+  // Patch a single updated source into every cached array IN PLACE, rather than
+  // invalidating + refetching the whole list. The full refetch was what locked
+  // the Subscriptions UI and collapsed the expanded row after every inline
+  // action (check / backfill / recover / toggle) — operator-flagged 2026-06-07.
+  // Map.set on a Vue-reactive ref(Map) triggers re-render; we hand each cache a
+  // NEW array so the table diffs just the one changed row.
+  function _patchSource(updated) {
+    if (!updated || updated.id == null) return
+    for (const [key, arr] of byArtist.value) {
+      const i = arr.findIndex((s) => s.id === updated.id)
+      if (i === -1) continue
+      const next = arr.slice()
+      next[i] = { ...arr[i], ...updated }
+      byArtist.value.set(key, next)
+    }
+  }
+
+  function _dropSource(id) {
+    for (const [key, arr] of byArtist.value) {
+      if (arr.some((s) => s.id === id)) {
+        byArtist.value.set(key, arr.filter((s) => s.id !== id))
+      }
+    }
+  }
+
   async function create(payload) {
     const body = await api.post('/api/sources', { body: payload })
     _invalidate(payload.artist_id)
@@ -40,13 +65,13 @@ export const useSourcesStore = defineStore('sources', () => {
 
   async function update(id, patch, artistIdHint = null) {
     const body = await api.patch(`/api/sources/${id}`, { body: patch })
-    _invalidate(artistIdHint ?? body.artist_id)
+    _patchSource(body)
     return body
   }
 
   async function remove(id, artistIdHint = null) {
     await api.delete(`/api/sources/${id}`)
-    _invalidate(artistIdHint)
+    _dropSource(id)
   }
 
   async function findOrCreateArtist(name) {
@@ -90,12 +115,12 @@ export const useSourcesStore = defineStore('sources', () => {
   // source shows backfill_state 'complete'); 'stop' cancels back to tick mode.
   async function startBackfill(id, artistIdHint = null) {
     const body = await api.post(`/api/sources/${id}/backfill`, { body: { action: 'start' } })
-    _invalidate(artistIdHint ?? body.artist_id)
+    _patchSource(body)
     return body
   }
   async function stopBackfill(id, artistIdHint = null) {
     const body = await api.post(`/api/sources/${id}/backfill`, { body: { action: 'stop' } })
-    _invalidate(artistIdHint ?? body.artist_id)
+    _patchSource(body)
     return body
   }
   // Plan #697: arm a recovery walk — a backfill that bypasses the Patreon
@@ -103,7 +128,7 @@ export const useSourcesStore = defineStore('sources', () => {
   // under the current pHash threshold. Stop with stopBackfill (shared lifecycle).
   async function recoverSource(id, artistIdHint = null) {
     const body = await api.post(`/api/sources/${id}/backfill`, { body: { action: 'recover' } })
-    _invalidate(artistIdHint ?? body.artist_id)
+    _patchSource(body)
     return body
   }