feat: Add AI-generated commit messages

Integrate Claude Haiku to automatically generate commit messages when
committing worktree changes. Shows a sparkle animation while generating
and auto-populates the commit message field.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

libs/git-utils/src/diff.ts

@@ -98,7 +98,7 @@ Binary file ${cleanPath} added
     const lines = content.split('\n');
 
     // Remove trailing empty line if the file ends with newline
-    if (lines.length > 0 && lines.at(-1) === '') {
+    if (lines.length > 0 && lines[lines.length - 1] === '') {
       lines.pop();
     }