fix(commit-commands): detect [gone] branches with git branch -vv in clean_gone

[AndrewDongminYoo]

Summary

/clean_gone never deletes anything because its [gone] detection is broken.

Root cause

The command lists branches with git branch -v and filters with grep '\[gone\]':

git branch -v | grep '\[gone\]' | sed 's/^[+* ]//' | awk '{print $1}'

Two problems:

1. git branch -v does not print the [gone] marker. The upstream-tracking
   state (including gone) is only emitted by git branch -vv (double v).
   With single -v the pipeline matches nothing.
2. The marker is never the literal [gone]. Git formats it as
   [origin/<branch>: gone], so grep '\[gone\]' would not match even with
   -vv.

Net effect: the loop body never runs and no stale branches are removed.

Fix

• List with git branch -vv (both in step 1 and the deletion pipeline).
• Match the real marker with grep ': gone]'.
• Minor hardening: sed 's/^[+* ]*//' (strip all leading */+/space markers)
  and clarifying comments.

git branch -vv | grep ': gone]' | sed 's/^[+* ]*//' | awk '{print $1}' | while read branch; do
  ...
done

Verification

Against git branch -vv style input:

  feat-a   1234567 [origin/feat-a: gone] msg
* main     89abcde [origin/main] msg
+ wt-br    abc1234 [origin/wt-br: gone] msg
  active   def5678 [origin/active: behind 2] msg

• Old logic (git branch -v | grep '\[gone\]'): 0 matches.
• New logic: outputs feat-a and wt-br only (correctly excludes main and the
  behind branch, and keeps the + worktree branch).

[RossMora]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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