feat: migrate from Node.js to Bun runtime

[jackbravo]

Summary

This is a rebase of #161 to merge cleanly with newest main branch.

Replace Node.js with Bun across host process and container agent for faster SQLite (bun:sqlite), native TypeScript execution, and cleaner process spawning (Bun.spawn, Bun.$)

Host: better-sqlite3 → bun:sqlite, child_process → Bun.spawn/$ shell, tsx → native Bun
Container: node:22-slim → oven/bun:slim, removes tsc build step, runs .ts directly

Test plan

• bun install succeeds and generates bun.lock
• bun run typecheck passes with zero errors
• bun run dev starts and connects to WhatsApp
• Reset container builder cache and run ./container/build.sh
• Verify container has source: container run -i --rm --entrypoint wc nanoclaw-agent:latest -l /app/src/index.ts
• Send a test message and verify agent responds
• Verify scheduled tasks still fire correctly
• Verify IPC message sending and task creation work

🤖 Generated with Claude Code

[TomGranot]

We're sticking with Node.js for now — migrating the entire runtime to Bun is too big a change and would break a lot of existing setups. Appreciate the work though @jackbravo!