feat: Users, Diagnostics and Tuning sit on the admin layout like the rest: debug mode is a row action on Users, every admin load error has Try again, and figures carry their scale (M503 #5608)

- Users: a one-line count of accounts, admins and open invites; Turn on/off debug mode in each row's actions, and a "debug on" badge that opens that account's events
- Diagnostics: no title or paragraph of its own; devices named by account, OS, app version and last seen, not client id; opens on ?account=
- Tuning: each profile, the taste build and Discover are row groups with one-line hints; the sparkline has a 0–100% axis
- Requests, Duplicates, Missing files and Suspect sources: load errors offer Try again
- Library: cover art reads "N of M albums have art"

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

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

@@ -164,7 +164,10 @@
   {#if query.isPending}
     <p class="text-text-secondary">Reading the queue…</p>
   {:else if query.isError}
-    <p class="text-error-fg">Couldn't load requests.</p>
+    <p class="text-sm text-error-fg">
+      Couldn't load the requests.
+      <button type="button" class="underline hover:no-underline" onclick={() => query.refetch()}>Try again</button>
+    </p>
   {:else if rows.length === 0}
     <p class="text-text-secondary">Nothing here.</p>
   {:else}