[Task 5] Fix lefthook.yml to preserve user commit messages

Implements:
- Updated prepare-commit-msg hook to check {2} parameter
- Hook only runs commitment when {2} is empty (regular commits)
- Preserves messages for git commit -m and merge commits
- Updated hook to use commands instead of jobs for consistency
- Added explanatory comments matching example hooks

Acceptance criteria met:
✅ lefthook.yml checks {2} parameter before running commitment
✅ git commit generates message (hook runs)
✅ git commit -m "test" preserves message (hook skips)
✅ Merge commits preserve messages (hook skips)
✅ commitment dogfooding still works
✅ Examples already correct (no changes needed)

Author: arittr

lefthook.yml

@@ -14,6 +14,9 @@ prepare-commit-msg:
   skip:
     - merge
     - rebase
-  jobs:
-    - run: ./dist/cli.js --message-only > {1}
+  commands:
+    commitment:
+      # Only run for regular commits (not merge, squash, or when message specified)
+      # {1} is the commit message file, {2} is the commit source
+      run: '[ -z "{2}" ] && ./dist/cli.js --message-only > {1} || true'
       interactive: true