feat: Admin is a left rail with how many wait on you in each queue, and the Overview opens with a verdict, the queues that need you and since when, then the clear ones on one line (M503 #5605)

- GET /api/admin/summary: every admin queue (requests, reported tracks,
  playback errors, duplicates, suspect sources, missing files) with its
  count and the age of its oldest item, in one query.
- The admin layout drops the 11-tab strip for SectionRail, as Settings and
  the Collection have, with each queue's count as its badge; the counts
  refresh on each admin navigation and every 30s.
- The Overview leads with "Nothing needs you." or "N things need you.",
  lists each waiting queue with "oldest 3d ago" and a link to it, counts a
  failed library scan as a problem, and names the empty queues on one line.
  The request and quarantine previews and the stat tiles are gone; those
  queues are worked on their own pages. A failed summary says so with Try
  again instead of reading as all-clear.

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

web/src/lib/components/AdminTabs.svelte

@@ -1,42 +0,0 @@
-<script lang="ts">
-  import { page } from '$app/state';
-
-  type Item = { href: string; label: string };
-
-  const items: Item[] = [
-    { href: '/admin',                 label: 'Overview'        },
-    { href: '/admin/integrations',    label: 'Integrations'    },
-    { href: '/admin/requests',        label: 'Requests'        },
-    { href: '/admin/quarantine',      label: 'Quarantine'      },
-    { href: '/admin/missing-files',   label: 'Missing files'   },
-    { href: '/admin/duplicates',      label: 'Duplicates'      },
-    { href: '/admin/suspect-sources', label: 'Suspect sources' },
-    { href: '/admin/playback-errors', label: 'Playback errors' },
-    { href: '/admin/diagnostics',     label: 'Diagnostics'     },
-    { href: '/admin/tuning',          label: 'Tuning'          },
-    { href: '/admin/users',           label: 'Users'           }
-  ];
-
-  function isActive(href: string): boolean {
-    if (href === '/admin') return page.url.pathname === '/admin';
-    return page.url.pathname.startsWith(href);
-  }
-</script>
-
-<nav aria-label="Admin sections" class="sticky top-0 z-10 border-b border-border bg-background">
-  <ul class="flex gap-2">
-    {#each items as item (item.href)}
-      <li>
-        <a
-          href={item.href}
-          aria-current={isActive(item.href) ? 'page' : undefined}
-          class="block border-b-2 px-3 py-2 text-sm transition-colors {isActive(item.href)
-            ? 'border-accent text-text-primary'
-            : 'border-transparent text-text-secondary hover:text-text-primary'}"
-        >
-          {item.label}
-        </a>
-      </li>
-    {/each}
-  </ul>
-</nav>

web/src/lib/components/AdminTabs.test.ts

@@ -1,79 +0,0 @@
-import { describe, expect, test, vi } from 'vitest';
-import { render, screen } from '@testing-library/svelte';
-import { pageUrlModule } from '#test-utils/mocks/appState.js';
-
-const state = vi.hoisted(() => ({
-  pageUrl: new URL('http://localhost/admin')
-}));
-
-vi.mock('$app/state', () => pageUrlModule(state));
-
-import AdminTabs from './AdminTabs.svelte';
-
-describe('AdminTabs', () => {
-  test('Overview tab is current when on /admin', () => {
-    state.pageUrl = new URL('http://localhost/admin');
-    render(AdminTabs);
-    const overview = screen.getByRole('link', { name: /overview/i });
-    expect(overview).toHaveAttribute('aria-current', 'page');
-  });
-
-  test('Integrations tab is current when on /admin/integrations', () => {
-    state.pageUrl = new URL('http://localhost/admin/integrations');
-    render(AdminTabs);
-    expect(screen.getByRole('link', { name: /integrations/i })).toHaveAttribute(
-      'aria-current',
-      'page'
-    );
-    expect(screen.getByRole('link', { name: /overview/i })).not.toHaveAttribute('aria-current');
-  });
-
-  test('Requests tab is current when on /admin/requests', () => {
-    state.pageUrl = new URL('http://localhost/admin/requests');
-    render(AdminTabs);
-    expect(screen.getByRole('link', { name: /requests/i })).toHaveAttribute('aria-current', 'page');
-  });
-
-  test('Quarantine tab is current when on /admin/quarantine', () => {
-    state.pageUrl = new URL('http://localhost/admin/quarantine');
-    render(AdminTabs);
-    expect(screen.getByRole('link', { name: /quarantine/i })).toHaveAttribute(
-      'aria-current',
-      'page'
-    );
-  });
-
-  test('Users tab is current when on /admin/users', () => {
-    state.pageUrl = new URL('http://localhost/admin/users');
-    render(AdminTabs);
-    expect(screen.getByRole('link', { name: /users/i })).toHaveAttribute(
-      'aria-current',
-      'page'
-    );
-  });
-
-  test('renders all eleven tabs in order', () => {
-    state.pageUrl = new URL('http://localhost/admin');
-    render(AdminTabs);
-    const links = screen.getAllByRole('link');
-    expect(links.map((l) => l.textContent?.trim())).toEqual([
-      'Overview',
-      'Integrations',
-      'Requests',
-      'Quarantine',
-      // Missing files sits with Quarantine and Playback errors: the three
-      // surfaces that show tracks needing an operator's attention.
-      'Missing files',
-      // Duplicates follows Missing files: both are library-health reports on
-      // what the library holds, rather than a queue of user reports.
-      'Duplicates',
-      // Suspect sources is the third library-health report: files whose
-      // names say they were ripped from a video.
-      'Suspect sources',
-      'Playback errors',
-      'Diagnostics',
-      'Tuning',
-      'Users'
-    ]);
-  });
-});

web/src/lib/components/TabStrip.svelte

@@ -1,7 +1,7 @@
 <script lang="ts" generics="Id extends string">
   // In-page tabs: one strip of buttons switching what a single page shows
-  // (#5416). The same look as AdminTabs and DiscoverTabs, which are route
-  // navigation and so stay links; this is for state inside one page, such as
+  // (#5416). The same look as DiscoverTabs, which is route
+  // navigation and so stays links; this is for state inside one page, such as
   // Liked's Artists | Albums | Tracks or a queue's status filter.
   type Item = {
     id: Id;