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/components/ai/Conversation.tsx

@@ -0,0 +1,117 @@
+import { useRef, useEffect, useState, createContext, useContext, useMemo, type ReactNode } from 'react';
+
+// ---------------------------------------------------------------------------
+// ConversationContext — shared state for child ai-elements components
+// ---------------------------------------------------------------------------
+
+interface ConversationContextValue {
+  isStreaming: boolean;
+  setIsStreaming: (v: boolean) => void;
+  messages: unknown[];
+  setMessages: (msgs: unknown[]) => void;
+}
+
+const ConversationContext = createContext<ConversationContextValue | null>(null);
+
+export function useConversationContext() {
+  const ctx = useContext(ConversationContext);
+  if (!ctx) {
+    throw new Error('useConversationContext must be used within ConversationProvider');
+  }
+  return ctx;
+}
+
+export function ConversationProvider({ children }: { children: ReactNode }) {
+  const [isStreaming, setIsStreaming] = useState(false);
+  const [messages, setMessages] = useState<unknown[]>([]);
+
+  const value = useMemo(
+    () => ({ isStreaming, setIsStreaming, messages, setMessages }),
+    [isStreaming, messages],
+  );
+
+  return (
+    <ConversationContext.Provider value={value}>
+      {children}
+    </ConversationContext.Provider>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Conversation container with auto-stick-to-bottom scroll behavior
+// ---------------------------------------------------------------------------
+
+/**
+ * Conversation container with auto-stick-to-bottom scroll behavior.
+ *
+ * Inspired by DeerFlow's use-stick-to-bottom pattern:
+ * - Stays pinned to bottom during streaming
+ * - Remembers user's scroll position when they scroll up
+ * - Auto-scrolls back to bottom on new content when near the bottom
+ */
+interface ConversationProps {
+  children: ReactNode;
+  className?: string;
+}
+
+const SCROLL_THRESHOLD = 80; // px from bottom to consider "at bottom"
+
+export function Conversation({ children, className = '' }: ConversationProps) {
+  const containerRef = useRef<HTMLDivElement>(null);
+  const isAtBottomRef = useRef(true);
+  const observerRef = useRef<ResizeObserver | null>(null);
+
+  // Track whether user is near the bottom
+  const handleScroll = () => {
+    const el = containerRef.current;
+    if (!el) return;
+    const distanceFromBottom = el.scrollHeight - el.scrollTop - el.clientHeight;
+    isAtBottomRef.current = distanceFromBottom < SCROLL_THRESHOLD;
+  };
+
+  // Auto-scroll to bottom when content changes and user is at bottom
+  useEffect(() => {
+    const el = containerRef.current;
+    if (!el) return;
+
+    observerRef.current = new ResizeObserver(() => {
+      if (isAtBottomRef.current) {
+        el.scrollTop = el.scrollHeight;
+      }
+    });
+
+    observerRef.current.observe(el);
+
+    return () => {
+      observerRef.current?.disconnect();
+    };
+  }, []);
+
+  // Also observe child list changes (new messages)
+  useEffect(() => {
+    const el = containerRef.current;
+    if (!el) return;
+
+    const mutationObserver = new MutationObserver(() => {
+      if (isAtBottomRef.current) {
+        el.scrollTop = el.scrollHeight;
+      }
+    });
+
+    mutationObserver.observe(el, { childList: true, subtree: true });
+
+    return () => {
+      mutationObserver.disconnect();
+    };
+  }, []);
+
+  return (
+    <div
+      ref={containerRef}
+      onScroll={handleScroll}
+      className={`overflow-y-auto custom-scrollbar ${className}`}
+    >
+      {children}
+    </div>
+  );
+}