feat(workers): runner loop + echo handler

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

workers/void_workers/handlers/echo.py

@@ -0,0 +1,5 @@
+NAME = "echo"
+
+
+def handle(job_data: dict) -> dict:
+    return {"pong": job_data.get("ping", 0)}