test(hygiene): close every brain the find suite creates

tests/integration/find-*.test.ts and tests/unit/brainy/find*.test.ts each
opened one or more Brainy instances (via beforeAll/beforeEach) and never
closed them — the leaked instance's cadence timer stays armed for the rest
of the single-forked vitest run and keeps narrating into every later file.

find-unified-integration.test.ts was a real bug, not just a missing hook:
its afterAll called a no-op TestCleanup().cleanup() (nothing was ever
registered with it) and then discarded the brain reference with
`brain = null` — the brain was never actually closed.

tests/integration/find-unified-integration.test.ts

@@ -48,6 +48,7 @@ describe('Unified Find() Integration Tests', () => {
 
   afterAll(async () => {
     await cleanup.cleanup()
+    await brain.close()
     brain = null as any
   })