feat: WSL distro enhancements — MOTD, CLI, auto-update, smaller tarball

[Awaiswilll]

Summary

Complete WSL distro enhancement: custom MOTD, dweb CLI, auto-update mechanism, and smaller tarball.

Changes

New: MOTD Banner (/etc/profile.d/dweb-motd.sh)

• dweb ASCII art logo on every wsl -d dweb login
• Shows server status (running/starting), Node.js version, memory, uptime, load, IP
• Lists available dweb commands

New: dweb CLI (/usr/bin/dweb)

• dweb status — detailed server + system status
• dweb start|stop|restart — manage the server
• dweb logs [-f] — view server logs
• dweb ping — quick health check
• dweb update — check for newer GitHub releases

New: Auto-update (/opt/dweb/tools/dweb-update.sh)

• Checks latest GitHub release
• Downloads and applies updates in-place (with backup)
• Invokable via dweb update

Smaller tarball

• Stripped: locales, zoneinfo, i18n, headers, static libs, .pyc caches
• Reduced from 57.6MB to 46MB (20% smaller)

Build script (build-wsl-distro.sh)

• Added overlay installation step for reproducible builds
• Overlay source files in packaging/wsl/overlay/

Testing

1. wsl --import dweb C:\dweb-wsl dweb-wsl-rootfs.tar.gz --version 2
2. wsl -d dweb — should show MOTD banner
3. dweb status — should show server info
4. dweb ping — should return {"status":"ok"}
5. dweb update — should check GitHub releases

Closes #4, #5