feat: add Pippin shell action button to worktree launch buttons

[malaporte]

Summary

Adds a new action button to each worktree card that opens a Ghostty terminal tab running pippin shell directly in the worktree directory. The button is only shown when pippin is available on the user's PATH.

Changes

• New launch:pippinShell RPC request and bun-side handler
• New launchPippinShell() launcher that resolves the pippin binary via the login-shell env, then opens a Ghostty tab with command set to the resolved path and the login-shell PATH injected as an environment variable (so tools like docker are available inside the session)
• New system:pippinPath RPC that probes which pippin at startup
• LaunchButtons component probes system:pippinPath on mount and conditionally renders the button using IconPrison
• Full test coverage for the new launcher, RPC, and conditional button rendering

Testing

• bun run test — 25 test files, 64 tests, all passing
• bun run typecheck — clean
• Manually verified: button opens Ghostty tab running pippin shell in the correct worktree directory; exiting Pippin closes the tab rather than dropping back to the default shell; button is hidden when pippin is not installed

Reviewer Notes

The launcher resolves the absolute pippin binary path via which pippin using the login-shell environment before constructing the AppleScript, because Ghostty's GUI process runs with a stripped PATH. The login-shell PATH is also forwarded as a surface environment variable so subprocesses spawned by Pippin (e.g. docker) can be found.

[github-actions]

🎉 This PR is included in version 2.10.0 🎉

The release is available on GitHub release

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