Replace mise dev tasks with concurrently for clean signal handling
mise's parallel task runner didn't propagate SIGINT cleanly, requiring
double Ctrl-C and leaving ghost node processes. Switched to concurrently
via pnpm scripts which handles process groups properly. Also added
.vite to .gitignore.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>