Add watch-folder mode and wire MCP/watcher into entrypoint

- New watcher.py: polls WATCH_DIR, enqueues transcription+summary via Celery.
- New process_watch_file_task in tasks.py.
- Updated __main__.py: WebUI always runs; MCP and watcher run in parallel when enabled.

scraibe/__main__.py

@@ -4,7 +4,9 @@ Entrypoint for running ScrAIbe as a module:
     python -m scraibe
 
 Always launches the Web GUI (Gradio).
-Optionally launches an MCP-style API server in parallel.
+Optionally launches:
+- MCP-style API server
+- Watch-folder mode
 """
 
 import os
@@ -38,5 +40,9 @@ if __name__ == "__main__":
         t = threading.Thread(target=_run_mcp_server, daemon=True)
         t.start()
 
+    # Optionally start watch-folder mode
+    from .watcher import start_watcher
+    start_watcher()
+
     # Always start WebUI (Gradio)
     create_app()