Spawns a notify watcher rooted at the panel root and refreshes entries on filesystem changes. Path-classification (`is_noisy_path`) filters out churn from typical workspace noise (`.git/objects`, `target/`, swap files), and `watcher_action` decides whether a raw event should rebuild entries, refresh VCS, or be ignored — both live as pure functions in a `watcher` submodule so the noisy-path boundaries and event-routing are unit-tested without a real watcher.