fix(skills): use git diff --stat HEAD and remove duplicate worktree cleanup

- git-commit: change `git diff --stat` to `git diff --stat HEAD` so both
  staged and unstaged changes are shown in the injected context
- pr-flow: remove duplicate `git worktree remove --force` block in the
  max-iterations path that would cause a spurious error on second removal

Co-Authored-By: Claude <noreply@anthropic.com>

Author: nkoji21

.agents/skills/git-commit/SKILL.md

@@ -13,7 +13,7 @@ Review current changes and autonomously commit following Conventional Commits.
 
 **Diff stat:**
 ```
-!`git diff --stat`
+!`git diff --stat HEAD`
 ```
 
 ## Arguments

.agents/skills/pr-flow/SKILL.md

@@ -110,10 +110,6 @@ Format findings as a markdown list. Each item: severity label (`must-fix` / `sug
     ```
     git worktree remove --force $WORKTREE_PATH
     ```
-  - Clean up the worktree:
-    ```
-    git worktree remove --force $WORKTREE_PATH
-    ```
   - Stop. Do NOT proceed to merge.
 
 ## Phase 5: LGTM + Merge