feat: add autosync daemon with file watching and launchd support

[nateGeorge]

Summary

Adds a background autosync daemon that keeps OpenCode config in sync automatically.

Features

• File watching: Watches ~/.config/opencode/ for changes via fsnotify (native kqueue on macOS)
• Periodic sync: Syncs on an interval (default: 5 minutes)
• Debouncing: Rapid changes are debounced (default: 3 seconds) to avoid excessive syncs
• Launchd integration: autosync install/uninstall/status commands manage a macOS launchd service
• Optional: Disabled by default; opt-in via config

New Commands

opencode-sync watch                 # Run daemon in foreground
opencode-sync autosync install      # Install as launchd service (macOS)
opencode-sync autosync uninstall    # Remove launchd service
opencode-sync autosync status       # Show service status + recent logs

New Config Section

{
  "autosync": {
    "enabled": false,
    "pollInterval": "5m",
    "debounceDelay": "3s",
    "watchFiles": true
  }
}

Design Notes

• The daemon runs sync (pull + push) on triggers
• File watcher uses fsnotify which uses native kqueue on macOS — no polling, no external deps
• The watch command can be run manually or via launchd
• Launchd plist uses KeepAlive so the daemon restarts if it crashes
• Logs go to ~/Library/Logs/opencode-sync/autosync.log

Testing

• go build ./... passes
• The watcher has been tested locally with manual file changes

Related

Inspired by the oc-sync plugin's auto-sync behavior, but implemented as a native CLI feature so it works without OpenCode running and supports any git host.