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-complement-operators.test.ts

@@ -7,7 +7,7 @@
  * soft-delete semantic: `field !== value` MUST include entities that have no
  * such field at all.
  */
-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'
 
@@ -26,6 +26,10 @@ describe('find() complement operators (ne / exists:false / missing:true)', () =>
     ids.noField2 = await brain.add({ data: 'n2', type: NounType.Thing, metadata: { other: 2 } })
   })
 
+  afterEach(async () => {
+    await brain.close()
+  })
+
   it('ne returns everything except the matching value — INCLUDING entities without the field', async () => {
     const rows = await brain.find({ where: { status: { ne: 'active' } }, limit: 100 })
     const got = new Set(rows.map((r) => r.id))