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/unit/brainy/find-index-integrity-guard.test.ts

@@ -12,7 +12,7 @@
  * returns an id whose record matches NEITHER the type nor the where filter) and
  * assert the phantom is dropped while the genuine matches survive.
  */
-import { describe, it, expect, beforeEach } from 'vitest'
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
 import { Brainy } from '../../../src/brainy'
 import { NounType } from '../../../src/types/graphTypes'
 
@@ -48,6 +48,10 @@ describe('find() index-integrity guard (phantom row class)', () => {
     })
   })
 
+  afterEach(async () => {
+    await brain.close()
+  })
+
   it('healthy index: the discriminant query returns only the staff Person', async () => {
     const rows = await brain.find({ type: NounType.Person, where: { entityType: 'staff' }, limit: 100 })
     expect(rows.map((r) => r.id)).toEqual([staffId])