New protocol:
- Windows binary scans directory (fast native NTFS) and sends manifest
- Container receives manifest, compares with local /data state
- Only copies files that differ (size, modtime, mode, symlink)

Protocol messages:
- manifest: sends full file metadata from Windows
- manifest_done: signals manifest transfer complete
- event_create/write/remove: file change events

Flow:
1. Container connects to socket
2. Windows binary sends manifest (file metadata)
3. Container scans /data (fast local volume)
4. Container copies only changed files from /host (9P bind mount)
5. Container enters event-waiting loop

This dramatically speeds up initial sync by avoiding slow 9P scans.

Architecture:
- Windows binary: watches files via ReadDirectoryChangesW (fsnotify),
  sends events as newline-delimited JSON over Unix domain socket
- Container: performs initial sync, then listens on socket for events
  from Windows watcher

New files:
- cmd_windows.go: Windows serve command (watcher + socket server)
- cmd_linux.go: Linux socket client + event listener
- types.go: shared FileEvent, FileMeta, Manifest types
- watcher_test_helper.go: inotify-based watcher for integration tests

Changes:
- main.go: simplified to just call run()
- watcher.go: removed fsnotify dependency, extracted Watcher interface
- sync.go: removed duplicate type definitions
- watcher_test.go: uses watchForTests() helper

Usage:
  sourcewatch.exe -dir C:\myproject -socket D:\sourcewatch.sock
  docker run -v D:\sourcewatch.sock:/run/sourcewatch.sock \
             -v C:\myproject:/host:ro -v mydata:/data sourcewatch