fix(424): add throttled field to all StoryAgent ctors and handle HardBlock in ws.rs

The initial commit added the `throttled` field to `StoryAgent` but missed
several construction sites in lifecycle.rs, test_helpers.rs, and scan.rs.
Also adds the `HardBlock` match arm in the WebSocket event conversion and
minor CSS/import ordering fixes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/agents/pool/lifecycle.rs

@@ -552,6 +552,7 @@ impl AgentPool {
             base_branch: None,
             completion: None,
             log_session_id: Some(log_session_id),
+            throttled: false,
         })
     }
 
@@ -676,6 +677,7 @@ impl AgentPool {
                                 base_branch: None,
                                 completion: None,
                                 log_session_id: None,
+                                throttled: false,
                             }
                         });
                     }