Grepai Watch Daemon

This handles the background daemon that keeps your code index fresh as you work. You run `grepai watch` once and it scans your entire codebase, chunks it into ~512 token segments, generates embeddings, then monitors for file changes in real time. The setup is straightforward with `--background` for daemon mode and `--status` to check on it. What I appreciate here is the OS-native file watching (FSEvents on macOS, inotify on Linux) and the debounce configuration that prevents your editor's multiple rapid writes from triggering constant reindexing. If you're using GrepAI for semantic code search, you'll want this running so your index doesn't go stale every time you save a file.