bug: stale/frozen worktree lane rewind is reported as generic force override instead of targeted diagnostic

## Summary

During a watched Spec Kitty session on 2026-06-04, retrospective analysis showed a forced lane override on WP02. The agent later classified it as a known frozen-worktree stale-state quirk on `move-task`, not a real guard failure.

The product currently records force transitions, and merge hollow-review warnings look at force-heavy histories. That is useful, but stale/frozen worktree repair cases need a targeted diagnostic so operators do not read them as review independence failures or arbitrary guard bypasses.

## Current behavior

`move-task` can emit forced backward/rewind transitions, and status snapshots track `force_count`.

Merge then warns about hollow reviews when `force_count >= 2` or reviewer self-approval events are present.

This lumps together different cases:

- real guard override
- self-review fallback
- reviewer rejection rewind
- stale/frozen worktree state repair

## Expected behavior

When `move-task` encounters or repairs stale/frozen worktree state, the event trail should preserve a machine-readable reason/category distinct from generic force override.

Possible shape:

```json
{
"force": true,
"reason": "stale_worktree_repair: ...",
"policy_metadata": {
"force_category": "stale_worktree_repair",
"diagnostic_code": "STALE_WORKTREE_REWIND_REPAIR"
}
}
```

## Acceptance criteria

- Add a reproduction fixture for the frozen/stale worktree rewind case that currently requires/records force.
- The emitted event has a distinct diagnostic/category.
- Merge hollow-review warning excludes or separately reports stale-worktree repair force events.
- `spec-kitty doctor` or status output gives a direct remediation for stale/frozen worktree state.

Start by tracing the move-task force transitions and the status snapshot force_count handling, then follow how merge produces hollow-review warnings. Reproduce the frozen/stale worktree rewind case, inspect the emitted event and the spec-kitty doctor or status output, and verify that the new diagnostic is distinct, warning behavior is separated, and remediation is shown.

Written by the indexing model from the issue text.