fix(ui): button overlap + Markdown rendering (BUG-012, BUG-013)

BUG-012: Move side panel toggle button below header (top-3 → top-[52px])
to avoid overlap with "详情" button in chat header.

BUG-013: Add rich Markdown component overrides to StreamingText:
- Code blocks: dark bg, border, rounded, overflow-x-auto
- Inline code: subtle bg highlight
- Tables: full borders, alternating header bg, proper padding
- Lists: disc/decimal markers, spacing
- Headings: proper hierarchy sizes
- Blockquotes: left border + subtle bg
- Links: blue underlined with hover

desktop/src/components/ai/ResizableChatLayout.tsx

@@ -66,7 +66,7 @@ export function ResizableChatLayout({
         {chatPanel}
         <button
           onClick={handleToggle}
-          className="absolute top-3 right-3 z-10 p-1.5 rounded-md bg-white/80 dark:bg-gray-800/80 border border-gray-200 dark:border-gray-700 text-gray-500 dark:text-gray-400 hover:text-gray-700 dark:hover:text-gray-200 hover:bg-white dark:hover:bg-gray-800 transition-colors shadow-sm"
+          className="absolute top-[52px] right-3 z-10 p-1.5 rounded-md bg-white/80 dark:bg-gray-800/80 border border-gray-200 dark:border-gray-700 text-gray-500 dark:text-gray-400 hover:text-gray-700 dark:hover:text-gray-200 hover:bg-white dark:hover:bg-gray-800 transition-colors shadow-sm"
           title="打开侧面板"
         >
           <PanelRightOpen className="w-4 h-4" />
@@ -91,7 +91,7 @@ export function ResizableChatLayout({
             {chatPanel}
             <button
               onClick={handleToggle}
-              className="absolute top-3 right-3 z-10 p-1.5 rounded-md bg-white/80 dark:bg-gray-800/80 border border-gray-200 dark:border-gray-700 text-gray-500 dark:text-gray-400 hover:text-gray-700 dark:hover:text-gray-200 hover:bg-white dark:hover:bg-gray-800 transition-colors shadow-sm"
+              className="absolute top-[52px] right-3 z-10 p-1.5 rounded-md bg-white/80 dark:bg-gray-800/80 border border-gray-200 dark:border-gray-700 text-gray-500 dark:text-gray-400 hover:text-gray-700 dark:hover:text-gray-200 hover:bg-white dark:hover:bg-gray-800 transition-colors shadow-sm"
               title="关闭侧面板"
             >
               <PanelRightClose className="w-4 h-4" />

desktop/src/components/ai/StreamingText.tsx

@@ -1,17 +1,13 @@
 import { useMemo, useRef, useEffect, useState } from 'react';
 import ReactMarkdown from 'react-markdown';
 import remarkGfm from 'remark-gfm';
+import type { Components } from 'react-markdown';
 
 /**
  * Streaming text with word-by-word reveal animation.
  *
- * Inspired by DeerFlow's Streamdown library:
- * - Splits streaming text into "words" at whitespace and CJK boundaries
- * - Each word gets a CSS fade-in animation
- * - Historical messages render statically (no animation overhead)
- *
- * For non-streaming content, falls back to react-markdown for full
- * markdown rendering including GFM tables, strikethrough, etc.
+ * For completed messages, renders full Markdown with styled components.
+ * For streaming messages, uses token-by-token animation.
  */
 
 interface StreamingTextProps {
@@ -22,6 +18,115 @@ interface StreamingTextProps {
   asMarkdown?: boolean;
 }
 
+// ---------------------------------------------------------------------------
+// Markdown component overrides for rich rendering
+// ---------------------------------------------------------------------------
+
+const markdownComponents: Components = {
+  // Code blocks (```...```)
+  pre({ children }) {
+    return (
+      <pre className="bg-gray-50 dark:bg-gray-900 rounded-lg p-4 overflow-x-auto text-sm leading-relaxed border border-gray-200 dark:border-gray-700 my-3">
+        {children}
+      </pre>
+    );
+  },
+  // Inline code (`...`)
+  code({ className, children, ...props }) {
+    // If it has a language class, it's inside a code block — render as block
+    const isBlock = className?.startsWith('language-');
+    if (isBlock) {
+      return (
+        <code className={`${className || ''} text-gray-800 dark:text-gray-200`} {...props}>
+          {children}
+        </code>
+      );
+    }
+    return (
+      <code className="bg-gray-100 dark:bg-gray-800 text-gray-700 dark:text-gray-300 px-1.5 py-0.5 rounded text-[0.9em] font-mono" {...props}>
+        {children}
+      </code>
+    );
+  },
+  // Tables
+  table({ children }) {
+    return (
+      <div className="overflow-x-auto my-3 -mx-1">
+        <table className="min-w-full border-collapse border border-gray-200 dark:border-gray-700 rounded-lg text-sm">
+          {children}
+        </table>
+      </div>
+    );
+  },
+  thead({ children }) {
+    return <thead className="bg-gray-50 dark:bg-gray-800/50">{children}</thead>;
+  },
+  th({ children }) {
+    return (
+      <th className="border border-gray-200 dark:border-gray-700 px-3 py-2 text-left font-semibold text-gray-700 dark:text-gray-300">
+        {children}
+      </th>
+    );
+  },
+  td({ children }) {
+    return (
+      <td className="border border-gray-200 dark:border-gray-700 px-3 py-2 text-gray-600 dark:text-gray-400">
+        {children}
+      </td>
+    );
+  },
+  // Unordered lists
+  ul({ children }) {
+    return <ul className="list-disc list-outside ml-5 my-2 space-y-1">{children}</ul>;
+  },
+  // Ordered lists
+  ol({ children }) {
+    return <ol className="list-decimal list-outside ml-5 my-2 space-y-1">{children}</ol>;
+  },
+  // List items
+  li({ children }) {
+    return <li className="leading-relaxed">{children}</li>;
+  },
+  // Headings
+  h1({ children }) {
+    return <h1 className="text-xl font-bold mt-5 mb-3 text-gray-900 dark:text-gray-100 first:mt-0">{children}</h1>;
+  },
+  h2({ children }) {
+    return <h2 className="text-lg font-bold mt-4 mb-2 text-gray-900 dark:text-gray-100 first:mt-0">{children}</h2>;
+  },
+  h3({ children }) {
+    return <h3 className="text-base font-semibold mt-3 mb-2 text-gray-900 dark:text-gray-100 first:mt-0">{children}</h3>;
+  },
+  // Blockquotes
+  blockquote({ children }) {
+    return (
+      <blockquote className="border-l-4 border-gray-300 dark:border-gray-600 pl-4 py-1 my-3 text-gray-600 dark:text-gray-400 italic bg-gray-50 dark:bg-gray-800/30 rounded-r-lg">
+        {children}
+      </blockquote>
+    );
+  },
+  // Paragraphs
+  p({ children }) {
+    return <p className="my-2 leading-relaxed first:mt-0 last:mb-0">{children}</p>;
+  },
+  // Links
+  a({ href, children }) {
+    return (
+      <a href={href} target="_blank" rel="noopener noreferrer" className="text-blue-600 dark:text-blue-400 underline hover:text-blue-800 dark:hover:text-blue-300">
+        {children}
+      </a>
+    );
+  },
+  // Horizontal rules
+  hr() {
+    return <hr className="my-4 border-gray-200 dark:border-gray-700" />;
+  },
+};
+
+// ---------------------------------------------------------------------------
+// Token splitter for streaming animation
+// ---------------------------------------------------------------------------
+
 // Split text into words at whitespace and CJK character boundaries
 function splitIntoTokens(text: string): string[] {
   const tokens: string[] = [];
@@ -40,7 +145,6 @@ function splitIntoTokens(text: string): string[] {
     const isWhitespace = /\s/.test(char);
 
     if (isCJK) {
-      // CJK chars are individual tokens
       if (current) {
         tokens.push(current);
         current = '';
@@ -60,17 +164,21 @@ function splitIntoTokens(text: string): string[] {
   return tokens;
 }
 
+// ---------------------------------------------------------------------------
+// Main component
+// ---------------------------------------------------------------------------
+
 export function StreamingText({
   content,
   isStreaming,
   className = '',
   asMarkdown = true,
 }: StreamingTextProps) {
-  // For completed messages, use full markdown rendering
+  // For completed messages, use full markdown rendering with styled components
   if (!isStreaming && asMarkdown) {
     return (
       <div className={`prose-sm prose-gray dark:prose-invert max-w-none ${className}`}>
-        <ReactMarkdown remarkPlugins={[remarkGfm]}>
+        <ReactMarkdown remarkPlugins={[remarkGfm]} components={markdownComponents}>
           {content}
         </ReactMarkdown>
       </div>
@@ -102,7 +210,6 @@ function StreamingTokenText({ content, className }: { content: string; className
     if (visibleCount >= tokens.length) return;
 
     const remaining = tokens.length - visibleCount;
-    // Batch reveal: show multiple tokens per frame for fast streaming
     const batchSize = Math.min(remaining, 3);
     const timer = requestAnimationFrame(() => {
       setVisibleCount(prev => Math.min(prev + batchSize, tokens.length));