Extensions can declare watch globs outside their own directory via
devSessionWatchConfig.paths (e.g. an admin extension's static_root, or a
function pointing at a shared sources tree). Today, files added there at
runtime aren't picked up: chokidar only watches the specific files
returned by globSync at start, not their parent directories.

This change:
- Computes the static prefix of every external watch glob (the longest
  leading path with no wildcards) and adds those prefixes to chokidar's
  watch list, deduped against the extension directories chokidar already
  watches recursively.
- Loosens discoverFileOwners to attribute paths by watch-pattern match
  rather than directory containment alone. Outside-dir paths are only
  attributed to extensions that explicitly opt in via
  devSessionWatchConfig, so the default '**/*' pattern doesn't pollute
  attribution for config-style extensions whose directory is the app
  root.
- Updates pathMatchesWatchPatterns to match against both the absolute
  path and the path relative to the extension directory, since
  devSessionWatchConfig patterns can be either form.