FN-6334: rescue db recovery corruption test

Rescues the database recovery corruption test by reducing its fixture size and removing its quarantine.

- Reduce recovery test fixture rows so sqlite3 .recover is not overfed while still corrupting a B-tree page.
- Re-enable packages/core/src/__tests__/db.test.ts in the core Vitest config.
- Remove the db recovery test entry from the quarantine ledger.

Files changed:
 packages/core/src/__tests__/db.test.ts | 5 +++--
 packages/core/vitest.config.ts         | 1 -
 scripts/lib/test-quarantine.json       | 5 -----
 3 files changed, 3 insertions(+), 8 deletions(-)

Fusion-Task-Id: FN-6334

Fusion-Task-Lineage: c4555976-fe98-4f25-a1b5-e70bfd991b16

scripts/lib/test-quarantine.json

@@ -51,11 +51,6 @@
       "reason": "Flake observed during FN-6324 verification: broad `pnpm test` failed with `Task FN-001 not found` after temp-root disappearance symptoms in adjacent core tests, alongside a leaked fusion-test-workers temp root. The task only changed agent role policy/settings/heartbeat routing, so this is unrelated temp redirect suite-order/concurrency sensitivity.",
       "quarantinedAt": "2026-06-12"
     },
-    {
-      "file": "packages/core/src/__tests__/db.test.ts",
-      "reason": "Flake observed during FN-6299 verification: broad `pnpm --filter @fusion/core test` timed out in `Database.recoverIfCorrupt startup guard > rebuilds a malformed database and preserves the corrupt original` after 15s; earlier `pnpm test` attempt SIGTERM'd the core package and leaked a fusion-test-workers temp dir. Follow-up FN-6334.",
-      "quarantinedAt": "2026-06-12"
-    },
     {
       "file": "packages/core/src/__tests__/store-create-summarize-deferred-hook.test.ts",
       "reason": "Flake observed during FN-6320 final broad `pnpm test`: `store-create.test.ts > TaskStore > createTask with title summarization > defers the task-created hook until store-managed summarize completes` timed out because the registered task-created hook had zero calls after the gated store-managed summarizer prompt was released. FN-6326 cross-check: the test passed twice standalone after FN-6313, and product code in `TaskStore.createTask` suppresses the synchronous hook only while `hasPendingSummarization` is true, then unconditionally refreshes the task and calls `invokeTaskCreatedHook(latestTask)` after `onSummarize` settles across success/null/throw branches. The broad/package load failure was therefore classified as suite-load/harness sensitivity rather than a confirmed product defect; the single flaky `it` was extracted so the rest of `store-create.test.ts` remains covered.",