feat(web/m7-coverage-gauge): coverage API client + query

Adds CoverageRollup type, getCoverageRollup() against
/api/admin/library/coverage, and createCoverageQuery() with the same
3s/30s pacing used by scan-status. New qk.coverage() key follows the
existing zero-arg tuple pattern. Vitest covers the GET path and the
empty-library zero-state plus the with_art + pending + settled = total
invariant.

web/src/lib/api/admin.coverage.test.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { getCoverageRollup, type CoverageRollup } from './admin';
+
+vi.mock('./client', () => ({
+  api: { get: vi.fn(), post: vi.fn() }
+}));
+
+import { api } from './client';
+
+describe('admin coverage API', () => {
+  beforeEach(() => vi.clearAllMocks());
+
+  it('getCoverageRollup GETs the correct path', async () => {
+    const sample: CoverageRollup = {
+      total: 18026,
+      with_art: 12400,
+      pending: 5400,
+      settled: 226,
+      pending_no_mbid: 320
+    };
+    (api.get as unknown as ReturnType<typeof vi.fn>).mockResolvedValueOnce(sample);
+    const got = await getCoverageRollup();
+    expect(api.get).toHaveBeenCalledWith('/api/admin/library/coverage');
+    expect(got).toEqual(sample);
+  });
+
+  it('returns zeros on an empty library', async () => {
+    const empty: CoverageRollup = {
+      total: 0,
+      with_art: 0,
+      pending: 0,
+      settled: 0,
+      pending_no_mbid: 0
+    };
+    (api.get as unknown as ReturnType<typeof vi.fn>).mockResolvedValueOnce(empty);
+    const got = await getCoverageRollup();
+    expect(got.total).toBe(0);
+    expect(got.with_art + got.pending + got.settled).toBe(got.total);
+  });
+});

web/src/lib/api/admin.ts

@@ -236,3 +236,29 @@ export function createScanStatusQuery() {
     refetchInterval: 3_000
   });
 }
+
+// Library coverage --------------------------------------------------------
+
+export type CoverageRollup = {
+  total: number;
+  with_art: number;
+  pending: number;
+  settled: number;
+  pending_no_mbid: number;
+};
+
+export async function getCoverageRollup(): Promise<CoverageRollup> {
+  return api.get<CoverageRollup>('/api/admin/library/coverage');
+}
+
+// Same pacing as scan-status — 3s while polling, 30s stale-time. The
+// query is cheap server-side (one aggregate per call) and we want
+// the gauge to tick during a scan.
+export function createCoverageQuery() {
+  return createQuery({
+    queryKey: qk.coverage(),
+    queryFn: getCoverageRollup,
+    staleTime: 30_000,
+    refetchInterval: 3_000
+  });
+}

web/src/lib/api/queries.ts

@@ -35,6 +35,7 @@ export const qk = {
   adminQuarantineActions: (limit?: number) =>
     ['adminQuarantineActions', { limit: limit ?? 50 }] as const,
   scanStatus:             ()              => ['scanStatus'] as const,
+  coverage:               ()              => ['coverage'] as const,
   suggestions:            (limit?: number) =>
     ['suggestions', { limit: limit ?? 12 }] as const,
   home:         ()                 => ['home'] as const,