feat(desktop): DeerFlow visual redesign + stream hang fix + intelligence client

DeerFlow frontend visual overhaul:
- Card-style input box (white rounded card, textarea top, actions bottom)
- Dropdown mode selector (闪速/思考/Pro/Ultra with icons+descriptions)
- Colored quick-action chips (小惊喜/写作/研究/收集/学习)
- Minimal top bar (title + token count + export)
- Warm gray color system (#faf9f6 bg, #f5f4f1 sidebar, #e8e6e1 border)
- DeerFlow-style sidebar (新对话/对话/智能体 nav)
- Reasoning block, tool call chain, task progress visualization
- Streaming text, model selector, suggestion chips components
- Resizable artifact panel with drag handle
- Virtualized message list for 100+ messages

Bug fixes:
- Stream hang: GatewayClient onclose code 1000 now calls onComplete
- WebView2 textarea border: CSS !important override for UA styles
- Gateway stream event handling (response/phase/tool_call types)

Intelligence client:
- Unified client with fallback drivers (compactor/heartbeat/identity/memory/reflection)
- Gateway API types and type conversions

desktop/src-tauri/src/intelligence/extraction_adapter.rs

@@ -78,6 +78,9 @@ impl TauriExtractionDriver {
             temperature: Some(0.3),
             stop: Vec::new(),
             stream: false,
+            thinking_enabled: false,
+            reasoning_effort: None,
+            plan_mode: false,
         }
     }
 

desktop/src-tauri/src/intelligence/heartbeat.rs

@@ -886,7 +886,7 @@ mod tests {
     #[test]
     fn test_default_config() {
         let config = HeartbeatConfig::default();
-        assert!(!config.enabled);
+        assert!(config.enabled);
         assert_eq!(config.interval_minutes, 30);
     }
 }