Fix git branch indicator not updating when branch changes

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Description

This PR fixes the issue where the git branch indicator in the bottom-left of the CLI TUI doesn't update when the git branch is changed.

Changes

• Added a new useGitBranch hook that polls for git branch changes every second
• Updated ResponsiveRepoDisplay component to use the new hook and re-render when the branch changes
• The branch indicator now updates automatically within 1 second of a branch change

How it works

The useGitBranch hook uses a polling mechanism with setInterval to check for branch changes every second. When a branch change is detected, it updates the React state, which triggers a re-render of the ResponsiveRepoDisplay component with the updated branch information.

Testing

The existing git branch tests should still pass. The fix can be manually tested by:

1. Starting the CLI in a git repository
2. Observing the current branch in the bottom-left status bar
3. Switching to a different branch in another terminal
4. Within 1 second, the TUI should update to show the new branch name

Fixes CON-4406

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This agent session was co-authored by nate and Continue.

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Summary by cubic

Fixes the stale git branch indicator in the CLI TUI; the bottom-left branch now updates within ~1s after switching branches. Addresses CON-4406.

• Bug Fixes
  • Added useGitBranch hook that polls for branch changes and updates state only when it changes.
  • Updated ResponsiveRepoDisplay to use the hook and include the branch in memo dependencies to trigger re-render.