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

.mam.env.example

@@ -98,13 +98,17 @@
 #default: (unset → reads ~/.grok/auth.json)
 # XAI_API_KEY=replace_me
 
-# Optional multi-provider API keys for OpenCode CLI (if ~/.local/share/opencode/auth.json is not present).
-#default: (unset → reads ~/.local/share/opencode/auth.json)
+# Optional multi-provider API keys for OpenCode CLI and OpenAI API key for Codex CLI.
+#default: (unset → reads ~/.local/share/opencode/auth.json or ~/.codex/auth.json)
 # ANTHROPIC_API_KEY=replace_me
 # OPENAI_API_KEY=replace_me
 # GEMINI_API_KEY=replace_me
 # GROQ_API_KEY=replace_me
 
+# Optional override for Codex CLI state / session directory.
+#default: $HOME/.codex
+# CODEX_HOME=$HOME/.codex
+
 # Optional inline JSON permissions configuration for OpenCode.
 #default: (unset → defaults to --auto CLI bypass)
 # OPENCODE_PERMISSION='{"*":"allow"}'