fix(extensions): make LOCAL_EXTENSIONS hot reload reliable in Docker

The local-extensions watcher previously surfaced spurious reloads under Docker on macOS (VirtioFS / osxfs generates inotify events on every read, not just writes), and rebuilds that wrote many files at once produced one restart per file. It also touched superset/__init__.py to trigger Flask's reloader, which then meant any Python read of that file also looked like a change and recursed.

Changes:

- Watcher only acts on FileCreated/Modified/Moved events, verifies the file content actually changed via SHA-256, and debounces to one trigger per second.
- Use a dedicated sentinel file (superset/extensions/.reload_trigger) that Python never reads, registered with Flask via --extra-files. The watcher ensures the sentinel exists on startup.
- Bootstrap excludes superset/__init__.py from the file watcher so the old trigger path can't reintroduce the loop.
- docker-compose mounts ./local_extensions:/app/local_extensions so the bind path matches LOCAL_EXTENSIONS in the dev superset_config.
- Extension content endpoint and FRONTEND_REGEX accept nested paths inside frontend/dist so extensions can serve worker / WASM / chunk subfolders.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker/docker-bootstrap.sh

@@ -80,7 +80,9 @@ case "${1}" in
     ;;
   app)
     echo "Starting web app (using development server)..."
-    flask run -p $PORT --reload --debugger --host=0.0.0.0 --exclude-patterns "*/node_modules/*:*/.venv/*:*/build/*:*/__pycache__/*:*/superset-frontend/*"
+    flask run -p $PORT --reload --debugger --host=0.0.0.0 \
+      --extra-files "/app/superset/extensions/.reload_trigger" \
+      --exclude-patterns "*/node_modules/*:*/.venv/*:*/build/*:*/__pycache__/*:*/superset-frontend/*:*/superset/__init__.py"
     ;;
   app-gunicorn)
     echo "Starting web app..."