feat(lemonade): allow commands to be wrapped via supervisor script

[abn]

This pull request adds support for directly executing commands passed as arguments to the lemonade-supervisor.sh script if the command exists in the PATH. It also updates the smoke test suite to verify this new behavior. The most important changes are:

Supervisor Script Enhancement:

• Updated lemonade-supervisor.sh to check if the first argument is a command available in the PATH and, if so, execute it directly using exec. This allows the supervisor script to act as a command dispatcher for known commands.

flatpak run ai.lemonade_server.Lemonade lemonade pull ...

Test Suite Updates:

• Added /app/bin to the PATH in the smoke test setup to ensure test commands can be found and executed.
• Introduced a new smoke test that verifies the supervisor script executes a command directly when it is present in the PATH, and ensures that the usual application processes (lemond, tray, app) are not started in this scenario.

[sofiageo]

Will make more tests later