fix: admin bugs from the audit: a playback-error delete no longer reports failure, a failed Overview load no longer reads as all-clear, and email settings can't be saved over with defaults (M503 #5604)

- Playback errors: Delete file stops resolving the error row the track
  deletion already took with it (ON DELETE CASCADE), which 404'd into
  "Delete failed".
- Overview: a queue that fails to load says so with Try again, and its tile
  shows a dash, not 0. Delete via Lidarr shows only for an album Lidarr
  holds while Lidarr is connected. An approve refreshes the Collection.
- Quarantine: Delete via Lidarr is in the row menu, so a phone reaches it;
  "1 report", not "1 reports".
- Duplicates: the Keep badge follows the copy picked.
- Integrations: provider save failures and load errors are said, not
  swallowed or shown as "No providers registered"; the Lidarr test catches
  a failed call; SMTP fills once and Save stays off until it has loaded.
  Lidarr's blurb says what it is still used for.
- Requests: release profiles point at Collection › Following.
- Library: an empty library sends an admin to Admin to run a scan, and
  tells anyone else the admin scans it, instead of opening Settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/routes/admin/requests/+page.svelte

@@ -255,7 +255,7 @@
 >
   <p class="-mt-2 text-sm text-text-secondary">
     The profile says which kinds of release following
-    {profileRow?.artist_name ?? 'this artist'} wants. Profiles are edited under Integrations.
+    {profileRow?.artist_name ?? 'this artist'} wants. Profiles are edited under <a href="/collection/following" class="underline hover:no-underline">Collection › Following</a>.
   </p>
 
   <label class="mt-4 block">