FN-8936: stabilize Planning Mode handoff tests

Stabilize live Proceed-action handoffs and re-admit the Planning Mode flow suite.

- Settle hydration and re-query the Proceed action before direct-create test clicks.
- Remove the Planning Mode test quarantine and record its rescue in the testing ledger.

Files changed:
 .../suite-only-flakes-observed-register.md           |  4 ++++
 docs/testing.md                                      |  3 +++
 .../PlanningModeModal.planning-flow.test.tsx         | 20 ++++++++++++++++----
 packages/dashboard/vitest.config.ts                  |  5 -----
 scripts/lib/test-quarantine.json                     |  5 -----
 5 files changed, 23 insertions(+), 14 deletions(-)

Fusion-Task-Id: FN-8936

Fusion-Task-Lineage: ed869b67-9394-458b-879c-54da0d7d327e

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

scripts/lib/test-quarantine.json

@@ -5,11 +5,6 @@
       "file": "packages/engine/src/__tests__/project-engine.test.ts",
       "reason": "FN-8811 observed B4/B5 workspace busy contention asserting a stale 60s cap while runtime schedules 120s, then the subprocess guard timed out on git remote; reproduced in isolation on 2026-08-06. Do not widen timing or weaken the assertion; restore only with a root-cause fix before the deletion deadline.",
       "quarantinedAt": "2026-08-06"
-    },
-    {
-      "file": "packages/dashboard/app/components/__tests__/PlanningModeModal.planning-flow.test.tsx",
-      "reason": "FN-8816 observed the previously registered direct task-handoff failure a second time in a loaded planning-flow run while the exact test passed in isolation. Quarantined under the deletion ratchet rather than weakening assertions or adding retries; delete by 2026-08-20 unless a root-cause rescue restores stable coverage.",
-      "quarantinedAt": "2026-08-06"
     }
   ]
 }