feat: add cleanup command to remove worktrees for merged branches

[timvw]

Summary

• Add new wt cleanup command that identifies and removes worktrees for merged branches
• Support --dry-run flag to preview what would be removed
• Support --force flag to remove all without interactive confirmation
• Default mode prompts for confirmation on each worktree
• Automatically runs git worktree prune after cleanup

Usage

# Preview what would be removed
wt cleanup --dry-run

# Remove all merged worktrees without prompting
wt cleanup --force

# Interactive mode (default) - confirm each removal
wt cleanup

Why

After merging feature branches, worktrees often accumulate. This command provides a built-in alternative to manual cleanup scripts, making it easier to keep worktree directories tidy.

Testing

• Added unit tests for getMergedBranches helper function
• Added E2E test that creates a temporary repo with a merged branch worktree and verifies cleanup works correctly
• All existing tests pass

[codecov]

Codecov Report

❌ Patch coverage is 63.38028% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 22.78%. Comparing base (01d5f7f) to head (0988384).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
main.go	63.38%	19 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
+ Coverage   17.64%   22.78%   +5.14%     
==========================================
  Files           3        3              
  Lines         958     1027      +69     
==========================================
+ Hits          169      234      +65     
+ Misses        767      759       -8     
- Partials       22       34      +12     

Files with missing lines	Coverage Δ
main.go	28.54% <63.38%> (+9.02%)	⬆️

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