fix: add frontend/src/lib/ to git (was ignored by /lib/ pattern)

The root .gitignore had `lib/` which matched frontend/src/lib/,
causing Docker build to fail with "Module not found: Can't resolve
'@/lib/utils'" and '@/lib/i18n'.

Changed to `/lib/` so it only ignores the Python lib at repo root.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

@@ -10,8 +10,8 @@ dist/
 downloads/
 eggs/
 .eggs/
-lib/
-lib64/
+/lib/
+/lib64/
 parts/
 sdist/
 var/