[thorwhalen]

Part of i2mint/caplinks#3: heed's review gate now uses caplinks 0.0.4 (AttemptGuard, JsonRecords, FileTexts) instead of its own copies. Behaviour unchanged: the gated-page tests pass as they were.

• Removes _JsonRecords and the hand-rolled _locked dict / two-limiter logic (net 29 lines in, 56 out); the guard is built lazily on the first unlock, so caplinks is still imported only when a record exists.
• heed[gate] and dev now need caplinks>=0.0.4.

Adversarial review (fresh Opus agent): ship. Checked: no valid heed id rejected by caplinks' stricter token rule, no fail-open path, lock-out equivalent, thread-safe, no dead code. It found that a dangling symlink at access/<id>.json was served open before (now 404, since FileTexts refuses symlinks) and that heed review revoke crashed on such a record (fixed: it is replaced, closed); test added; comment corrected; one-use helper inlined. Side effect: the records folder is now 0700 and writes are fsynced.