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-create/SKILL.md

@@ -143,7 +143,7 @@ herdr_sessions:
 
 ```bash
 WORKSPACE=/path/to/project
-AGENT=claude  # or agy
+AGENT=claude  # claude | agy | hermes | cline — always pass it explicitly
 source .agents/skills/lib.sh
 SESSION_NAME="$(derive_session_name "$WORKSPACE" "$AGENT")"
 
@@ -168,7 +168,7 @@ case "$AGENT" in
   agy)
     herdr new-session -d -s "$SESSION_NAME" -x 140 -y 40 -c "$WORKSPACE" "agy --dangerously-skip-permissions"
     ;;
-  *) echo "ERROR: --agent must be claude or agy, got: $AGENT"; exit 2 ;;
+  *) echo "ERROR: --agent must be claude, agy, hermes or cline, got: $AGENT"; exit 2 ;;
 esac
 
 # 3. Wait for agent TUI to be ready (varies: claude ~5s, agy ~3s)