PICH Lab Mac preview 0.14.0

The native launcher starts a bundled Python backend on loopback, opens the app
in the default browser, and interrupts that child when the launcher quits.
No separately installed Python, Codex runtime, or developer tools are required
on the user's Mac. DAW bridges are lazy: Find starts a bridge when needed.
This does not automate each DAW's first-time controller configuration.

Build: Python 3 venv, PyInstaller 6.22.0, Apple command-line tools.
Run: python desktop/build.py from any directory.
Build creates outputs/pich-key-lab-release/PICH Lab.app.
Move a previous release aside before building; the script never overwrites it.
Apple silicon only; locally signed. Clean-Mac compatibility and Developer ID
signing/notarization are pending. Never strip quarantine as an installation step.

Sources are bundled under backend/_internal/source and host-specific folders.
Documentation: https://pyinstaller.org/en/stable/usage.html

Key-file handling: .pichkey is registered as JSON data. The launcher validates
format/version/key/scale and forwards them to its own local browser URL fragment.
It never sends to Auto-Tune automatically. The fragment is removed after reading.
