Add dirty branch launch safety gate

[tonythethompson]

The current QuickShell launch flow can block a workspace launch when the workspace would switch branches and the worktree is dirty. The Raycast backlog should keep that safety behavior so the port does not silently remove an existing guardrail.

Acceptance criteria:

• Launch can be blocked when branch switching would occur on a dirty worktree.
• The user gets a clear message explaining why launch was blocked.
• The behavior can be configured from settings.
• The gate applies before launch starts, not after the terminal is already opened.