Fix Finder-launched auth environment

[dr-baker]

Summary

Hydrate the main-process environment from the user's login shell on macOS before publishing auth/model status.

When Zenbu is launched from Finder/Dock, macOS provides a reduced environment. In that state the model list appears, but selecting a model does not persist and sending messages fails silently. Launching the same app from Terminal works because it inherits the shell environment.

This uses the existing shell-env dependency and runs once during AuthService.evaluate() before the Pi auth storage/model registry publishes provider status.

Repro

1. Start from a fresh Zenbu install, or clear any previously selected chat model.
2. Configure auth in a way that works from the user's shell environment.
3. Launch Zenbu from Finder/Dock.
4. Open a chat.
5. Try selecting a model from the model picker.
6. Send a message.

Expected: the model selection persists and the message starts an agent turn.

Actual: the model list appears, but selecting a model does not stick, and sending a message clears/fails without an agent response.

Then launch the same app from Terminal:

/Applications/Zenbu.app/Contents/MacOS/Zenbu

The model picker and message sending work.

Testing

• Typechecked the patched installed copy:

  cd ~/.zenbu/apps/zenbu-env-test
  ./node_modules/.bin/tsc --noEmit

• Verified with a Finder-launched wrapper app pointed at an isolated patched source copy:

  • Model selection persists.
  • Sending a message starts the agent instead of failing silently.