feat(web): AcoustID card on Integrations — key, threshold, coverage by source (M401 #3922)

The card takes the slot of the unimplemented "MusicBrainz overrides"
placeholder. Rows:
- the on switch
- a write-only key field (the stored key is never sent back), with a
  link to register an application
- the minimum score (0.5 to 1)

Below them, recording-id coverage reads as a column: from tags, looked
up, none, and of the none how many are waiting, no match, ambiguous or
failed. There is a "Look up now" button and a folded list of the tracks
the lookup could not settle.

Off, keyless and stopped-short passes are each a visible state with the
reason (rule 164).

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

web/src/routes/admin/integrations/integrations.test.ts

@@ -28,7 +28,12 @@ vi.mock('$lib/api/admin', () => ({
   testTagProvider: vi.fn(),
   createSMTPConfigQuery: vi.fn(),
   updateSMTPConfig: vi.fn(),
-  testSMTPConfig: vi.fn()
+  testSMTPConfig: vi.fn(),
+  // AcoustIDCard loads on mount; a never-settling read leaves it on "Loading…".
+  getAcoustID: vi.fn(() => new Promise(() => {})),
+  updateAcoustIDSettings: vi.fn(),
+  runAcoustIDLookup: vi.fn(),
+  listUnsettledAcoustID: vi.fn()
 }));
 
 import IntegrationsPage from './+page.svelte';