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

Each file opened one or more Brainy instances (beforeEach, or a small
per-test helper like migration-gate-family-scoped's module-level seed())
and never closed them. migration-gate-family-scoped.test.ts now tracks
every brain seed() hands back in a describe-scoped array drained by
afterEach, since the helper itself lives outside the describe block.

tests/unit/graph/graph-fastpath-honest-readiness.test.ts

@@ -8,7 +8,7 @@
  * scan; and a one-shot probe self-heals a no-isReady provider whose adjacency
  * did not cold-load.
  */
-import { describe, it, expect, beforeEach } from 'vitest'
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
 import { Brainy, NounType, VerbType } from '../../../src/index.js'
 
 describe('graph fast-path honest readiness (Finding 2)', () => {
@@ -33,6 +33,10 @@ describe('graph fast-path honest readiness (Finding 2)', () => {
     await storage.getVerbsBySource(a)
   })
 
+  afterEach(async () => {
+    await brain.close()
+  })
+
   it('not-ready provider → shard scan returns the REAL edges, not a silent []', async () => {
     const gi = storage.graphIndex
     // Simulate a cold native provider: count/manifest loaded (isInitialized) but