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/hooks/index.ts

@@ -15,3 +15,5 @@ export type {
   UseAutomationEventsOptions,
 } from './useAutomationEvents';
 
+export { useOptimisticMessages } from './useOptimisticMessages';
+

desktop/src/hooks/useOptimisticMessages.ts

@@ -0,0 +1,102 @@
+import { useCallback, useRef } from 'react';
+import { useChatStore, type Message } from '../store/chatStore';
+import { createLogger } from '../lib/logger';
+
+const log = createLogger('OptimisticMessages');
+
+/**
+ * Represents a file attached to an optimistic message,
+ * tracking its upload lifecycle. Extends MessageFile with a status field.
+ */
+interface OptimisticFile {
+  name: string;
+  size: number;
+  status: 'uploading' | 'uploaded' | 'error';
+  url?: string;
+}
+
+/**
+ * 3-phase optimistic message merging hook (inspired by DeerFlow useThreadStream).
+ *
+ * Phase 1: Instant local echo -- creates a synthetic user message with `optimistic: true`
+ * Phase 2: Server confirmation -- removes optimistic message when real message arrives
+ * Phase 3: File status transition -- updates file status from uploading -> uploaded | error
+ *
+ * This hook provides standalone utilities for components that need fine-grained
+ * control over optimistic rendering outside the main chat flow.
+ */
+export function useOptimisticMessages() {
+  const optimisticIdCounter = useRef(0);
+
+  const generateOptimisticId = useCallback(() => {
+    optimisticIdCounter.current += 1;
+    return `opt-user-${Date.now()}-${optimisticIdCounter.current}`;
+  }, []);
+
+  /**
+   * Phase 1: Create and insert an optimistic user message into the store.
+   * Returns the optimistic ID for later correlation.
+   */
+  const addOptimistic = useCallback((content: string, files?: File[]) => {
+    const id = generateOptimisticId();
+    const optimisticFiles: OptimisticFile[] | undefined = files?.map(f => ({
+      name: f.name,
+      size: f.size,
+      status: 'uploading' as const,
+    }));
+
+    const optimisticMessage: Message = {
+      id,
+      role: 'user',
+      content,
+      timestamp: new Date(),
+      optimistic: true,
+      // Cast through unknown because OptimisticFile extends MessageFile with status
+      files: optimisticFiles as Message['files'],
+    };
+
+    log.debug('Adding optimistic message', { id, content: content.slice(0, 50) });
+
+    useChatStore.setState(state => ({
+      messages: [...state.messages, optimisticMessage],
+    }));
+
+    return id;
+  }, [generateOptimisticId]);
+
+  /**
+   * Phase 2: Remove an optimistic message when the server confirms
+   * by sending back the real message.
+   */
+  const clearOnConfirm = useCallback((optimisticId: string) => {
+    log.debug('Clearing optimistic message on confirm', { optimisticId });
+
+    useChatStore.setState(state => ({
+      messages: state.messages.filter(m => m.id !== optimisticId),
+    }));
+  }, []);
+
+  /**
+   * Phase 3: Transition file attachment status for an optimistic message.
+   */
+  const updateFileStatus = useCallback((optimisticId: string, status: 'uploaded' | 'error') => {
+    log.debug('Updating file status', { optimisticId, status });
+
+    useChatStore.setState(state => ({
+      messages: state.messages.map(m => {
+        if (m.id === optimisticId && m.files) {
+          return {
+            ...m,
+            files: m.files.map(f => ({
+              ...f,
+              status,
+            })),
+          };
+        }
+        return m;
+      }),
+    }));
+  }, []);
+
+  return { addOptimistic, clearOnConfirm, updateFileStatus };
+}