refactor: standardize --agent option usage, improve YAML registry fallback, and fix layout falsy-zero trap (J-1)

- In stop_session.sh and update_yaml_resumed.sh: standardize explicit --agent option and use resolve_agent_type_from_registry to read agent type from YAML/DB state rather than brittle suffix-only regex inference.
- Update multi-agent-mux-stop/SKILL.md, multi-agent-mux-resume/SKILL.md, multi-agent-mux-create/SKILL.md, and deploy/INSTALL.md to standardize passing --agent explicitly.
- Fix J-1 in layout.py: refactor _env_int(*names, default=None) to take an explicit default parameter, eliminating the falsy-zero trap so MAM_MIN_PANE_COLS=0 is respected.
- Add regression and contract tests: test_j1_env_zero_min_cols_matches_flag_zero, test_j1_env_zero_min_rows_matches_flag_zero, test_comp_stop_agent_fallback_*, test_comp_docs_stop_examples_pass_agent.
- Verified 100% UNANIMOUS PASS from Planner claude and Reviewers claude and cline.

.agents/skills/multi-agent-mux-resume/scripts/resolve_session_id.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 # resolve_session_id.sh — multi-agent-mux-resume 의 부속 스크립트
 # Usage:
-#   bash resolve_session_id.sh --workspace <path> --agent <claude|agy>
+#   bash resolve_session_id.sh --workspace <path> --agent <claude|agy|hermes|cline>
 # 출력: stdout 으로 UUID 한 줄 (없으면 빈 줄 + exit 0)
 #
 # P0-C: 전역 agent_identities 를 즉시 반환하지 않는다. lib.sh::find_workspace_uuid