Harden mqlaunch release readiness

[MCamner]

Summary

• fix mqlaunch selftest exit-code propagation and update MQ boundary smoke assertions
• add command docs drift smoke coverage and route documented direct commands before AI fallback
• add CI coverage for the mqlaunch smoke suite and B2 Python tests
• add pytest dev requirements and remove tracked Python cache artifact
• include Excalidraw launcher/menu wiring and improve headless palette behavior

Verification

• MACOS_SCRIPTS_HOME=/Users/mansys/macos-scripts MQ_NO_TUI=1 tools/scripts/test-all.sh
• MACOS_SCRIPTS_HOME=/Users/mansys/macos-scripts MQ_NO_TUI=1 bin/mqlaunch selftest
• /private/tmp/macos-scripts-pytest-venv/bin/python -m pytest mqlaunch/b2_tui/tests
• zsh -n terminal/launchers/mqlaunch.sh
• MACOS_SCRIPTS_HOME=/Users/mansys/macos-scripts MQ_NO_TUI=1 bin/mqlaunch palette