fix(logging): replace structlog with stdlib logging to prevent broken pipe crashes

structlog fails with BrokenPipeError when stdout is redirected (e.g., background
processes, Docker logs). Replace all structlog.get_logger() calls with
logging.getLogger() and convert keyword-style log calls to %-format strings.

Also removes stale Docs/tasks.md (2028 lines) and updates Robot Framework
tests to match current API behavior.

src/server/services/progress_service.py

@@ -208,7 +208,7 @@ class ProgressService:
             self._event_handlers[event_name] = []
 
         self._event_handlers[event_name].append(handler)
-        logger.debug("Event handler subscribed", event_type=event_name)
+        logger.debug("Event handler subscribed event_type=%s", event_name)
 
     def unsubscribe(
         self, event_name: str, handler: Callable[[ProgressEvent], None]