feat: add PID lockfile guard to prevent duplicate instances

[Lafunamor]

Summary

• Adds acquirePidLock() called at the very start of main() that writes the current process PID to data/nanoclaw.pid
• If the lock file already exists and the recorded process is still alive, NanoClaw logs an error and exits immediately — preventing two instances from corrupting shared state (SQLite WAL, IPC directories, credential files)
• Stale lock files (process no longer running) are silently cleaned up and overwritten
• The lock file is removed automatically via a process.on('exit') handler on clean shutdown

Motivation

Running npm run dev twice, or a service manager restarting before a previous instance fully exits, leads to two NanoClaw processes racing on the same SQLite database and IPC queues. The PID lock is a lightweight, dependency-free safeguard.

Files changed

• src/index.ts — adds DATA_DIR import, acquirePidLock() function (~25 lines), and a single call in main()

Test plan

• Start NanoClaw normally — verifies data/nanoclaw.pid is written with the correct PID
• Start a second instance while the first is running — verifies it exits immediately with an error log
• Kill the first instance ungracefully (kill -9), then start again — verifies the stale lock file is cleaned up and startup succeeds
• Graceful shutdown (SIGTERM) — verifies the PID file is removed on exit

🤖 Generated with Claude Code

[gavrielc]

Closing as part of a stale issue/PR cleanup. If this is still relevant, please reopen and we'll take another look.