[FEATURE] Status bar should show uncommitted changes instead of branch diff

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The status bar displays the line diff between the current branch and the detected "main branch" (e.g., +77401 -1942). When working on a long-lived development branch that has diverged significantly from the main branch, this number is extremely large and misleading. Users cannot tell how many lines were actually modified in the current editing session.

Proposed Solution

Show uncommitted working tree changes (staged + unstaged, equivalent to git diff --stat) instead of the branch-level diff. This way users can track how many lines the current session has actually modified.

Alternatively, provide an option to toggle between "branch diff" and "working tree diff".

Alternative Solutions

Currently I manually run git diff --stat in the terminal to check actual uncommitted changes. The status bar number is ignored as it only reflects branch-level divergence.

Priority

Low - Nice to have

Feature Category

Interactive mode (TUI)

Use Case Example

1. I work on a long-lived feature branch that has diverged 77,000+ lines from the main branch
2. During a session, I only edit 2 files with +37 -35 lines changed
3. The status bar shows +77401 -1942, which reflects the entire branch history
4. I cannot tell from the UI how many lines my current session has actually modified
5. I have to run git diff --stat manually to get the real number

Additional Context

_No response_