Add setting to toggle git branch in shell prompt

[andersRuge]

Needs to be tested before I am ready for a review.

Summary

• Adds a toggle under Settings > Shell Terminal to show/hide the git branch in the terminal prompt
• Useful when working in worktrees where the branch name already appears in the directory path
• Default: on (preserves current behavior)
• Applies to new terminal sessions

Test plan

• Open Settings > General > Shell Terminal
• Toggle "Show git branch in prompt" off
• Open a new shell terminal — branch name should not appear in prompt
• Toggle back on, open new terminal — branch should reappear
• Verify toggle only shows when shell drawer is enabled