FN-6447: rescue session reconnect teardown

Rescue the session reconnect SSE test by shutting down route-owned background work before temp cleanup.

- Isolate the focused API harness from TaskStore EventEmitter startup workers.
- Dispose API routes and scheduled AI session cleanup before deleting the test temp root.
- Remove session-reconnect from the dashboard quarantine ledger and vitest skip list.

Files changed:
 .../src/__tests__/session-reconnect.test.ts        | 22 ++++++++++++++++++----
 packages/dashboard/vitest.config.ts                |  6 ++++--
 scripts/lib/test-quarantine.json                   |  5 -----
 3 files changed, 22 insertions(+), 11 deletions(-)

Fusion-Task-Id: FN-6447

Fusion-Task-Lineage: a3fef28c-b92b-4f47-9181-a63bb31e4f48

scripts/lib/test-quarantine.json

@@ -65,11 +65,6 @@
       "file": "packages/dashboard/src/__tests__/planning.test.ts",
       "reason": "FN-6444: orphaned dashboard planning route/API test is slow and fails standalone across stale agent/session mocks plus temp cleanup leakage. Quarantined instead of widening waits/timeouts or weakening assertions.",
       "quarantinedAt": "2026-06-14"
-    },
-    {
-      "file": "packages/dashboard/src/__tests__/session-reconnect.test.ts",
-      "reason": "FN-6444/FN-6447: dashboard API backfill shard 1 observed ENOTEMPTY temp cleanup leakage while replaying planning buffered events. Quarantined on sight for focused rescue/delete review instead of adding waits or weakening assertions.",
-      "quarantinedAt": "2026-06-14"
     }
   ]
 }