Add worktree status tracking to list command

[agarcher]

Summary

• Add enhanced status information to wt list showing commits ahead/behind main branch with ↑↓ arrows
• Show [uncommitted], [new], or [merged] status indicators with clear priority
• Store worktree creation metadata (timestamp and initial commit) in git config
• Add -v/--verbose flag for detailed multi-line output including worktree age
• Add STATUS column header in compact list output

Status Priority

New worktrees that haven't had any changes committed show [new] instead of being incorrectly marked as [merged]. The status priority is:

1. [uncommitted] - has uncommitted changes
2. [new] - still on initial commit (no changes committed yet)
3. [merged] - branch has been merged to main

Example Output

Compact (default):

  NAME                  BRANCH                         STATUS
* my-feature           feature/foo                    [new]
  with-changes         feature/bar                    ↑1 [uncommitted]
  done-branch          feature/baz                    [merged]

Verbose (-v):

================================================================================
* my-feature
  Branch: feature/foo
  Age: 3 days
  Status: new
================================================================================

Test plan

• All existing tests pass
• New tests for initial commit storage and IsNew status
• make lint passes
• make build succeeds

🤖 Generated with Claude Code