fix(doctor): categorize timeline_coverage as a brain check (takeover of #2817)

Only the doctor-categories half of #2817 — the auto_chronicle config
registration already landed on master via another PR. timeline_coverage
is emitted by src/core/onboard/checks.ts but was missing from
BRAIN_CHECK_NAMES, so it fell through the warn-once unknown-name path
to 'meta'.

Co-authored-by: davidfragnoli-lang <davidfragnoli-lang@users.noreply.github.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/core/doctor-categories.ts

@@ -103,6 +103,7 @@ export const BRAIN_CHECK_NAMES: ReadonlySet<string> = new Set([
   'sync_failures',
   'sync_freshness',
   'takes_weight_grid',
+  'timeline_coverage',
   'unified_multimodal_coverage',
   'voice_gate_health',
 ]);

test/doctor-categories.test.ts

@@ -124,6 +124,10 @@ describe('categorizeCheck', () => {
     expect(categorizeCheck('sync_freshness')).toBe('brain');
   });
 
+  test('timeline_coverage (emitted by onboard/checks.ts, not doctor.ts) is brain, not meta fallthrough (#2817)', () => {
+    expect(categorizeCheck('timeline_coverage')).toBe('brain');
+  });
+
   test('returns the right category for a known skill name', () => {
     expect(categorizeCheck('resolver_health')).toBe('skill');
     expect(categorizeCheck('skill_conformance')).toBe('skill');