fix(mqtt): resolve B-9 by implementing lazy get_logs_dir() evaluation

- Replace import-time LOGS_DIR cwd binding with dynamic get_logs_dir() function
- Implement PEP 562 __getattr__ and __dir__ for transparent LOGS_DIR backward compatibility
- Update audit-log callers in mqtt_common.py and registry.py to use dynamic resolution
- Add 5 regression guards in tests/test_tier1_unit.py (276/276 PASS)
- Update IMPROVEMENTS.md, VERSIONS.md, registry.md, and include plan and peer review reports

.agents/skills/multi-agent-mux-delegate-job/registry.md

@@ -165,7 +165,9 @@ even after the registry dir is cleaned up. It is git-ignored.
 | event received | `received` | `job_subscriber.py` |
 
 Helpers live in [`./scripts/mqtt_common.py`](./scripts/mqtt_common.py):
-`LOGS_DIR`, `job_log_path`, `init_job_log`, `append_event` (fcntl-locked,
+`get_logs_dir` (audit-log root, resolved per call — a chdir after import no
+longer strands the trail; `LOGS_DIR` remains as a dynamic compat alias),
+`job_log_path`, `init_job_log`, `append_event` (fcntl-locked,
 concurrent-append safe), `update_logged_status`, and the readers
 `read_logged_meta` / `read_logged_status` / `iter_logged_events` /
 `list_logged_jobs`. Every writer is **best-effort and isolated** — wrapped in