feat(agent): add full codex agent support (v4.2.0)

- Implement CodexAdapter in lib_py/agents/adapters/codex.py with safe flags and TUI readiness
- Extend create_session, resume_session, stop_session, and reconcile for codex CLI
- Support codex agent delegation and loop integration across all multi-agent skills
- Add unit, component, and contract test suites for codex integration
- Verify all 462 tests passing cleanly

.agents/skills/multi-agent-mux-stop/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: multi-agent-mux-stop
 description: "Stop an agent herdr session (claude, antigravity/agy) and update .mam/agent-sessions.yaml. Default stops gracefully and marks status=stopped with conversation preserved for resume. Does NOT delete on-disk conversation artifacts (jsonl/db) — those are preserved unless --purge-conversation is passed. Use when ending a work session, switching to a different one, or cleaning up before a fresh start."
-version: 4.1.3
+version: 4.2.0
 author: godopu
 license: MIT
 platforms: [linux, macos]
@@ -37,7 +37,7 @@ The stop command is always **graceful by default**:
 
 ```bash
 SESSION_NAME=<workspace>-creator-<agent>  # convention
-AGENT=claude                              # claude | agy | hermes | grok | opencode — always pass it
+AGENT=claude                              # claude | agy | hermes | grok | opencode | codex — always pass it
 AGENT_SESSIONS_YAML=.mam/agent-sessions.yaml
 
 # 1) Session is registered?