refactor(chat): 全屏/半屏切换移入 ChatPanel 内部

- Header 恢复单个"AI 问答"按钮，点击默认打开半屏模式
- ChatPanel 头部新增全屏/半屏切换按钮（Maximize2/Minimize2 图标）
- 半屏：markdown 与问答并排各占一半
- 全屏：问答占满内容区，隐藏 markdown

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

BillNote_frontend/src/pages/HomePage/components/ChatPanel.tsx

@@ -3,14 +3,18 @@ import { Bubble, Sender } from '@ant-design/x'
 import type { BubbleProps } from '@ant-design/x'
 import { Button } from '@/components/ui/button'
 import { Badge } from '@/components/ui/badge'
-import { Loader2, Trash2, ChevronDown, ChevronUp, BookOpen, UserRound, Bot } from 'lucide-react'
+import { Loader2, Trash2, ChevronDown, ChevronUp, BookOpen, UserRound, Bot, Maximize2, Minimize2 } from 'lucide-react'
 import { toast } from 'react-hot-toast'
 import { useChatStore } from '@/store/chatStore'
 import { useTaskStore } from '@/store/taskStore'
 import { askQuestion, getChatStatus, indexTask, type ChatSource, type IndexStatus } from '@/services/chat'
 
+type ChatMode = 'half' | 'full'
+
 interface ChatPanelProps {
   taskId: string
+  mode: ChatMode
+  onModeChange: (mode: ChatMode) => void
 }
 
 function SourceBadges({ sources }: { sources: ChatSource[] }) {
@@ -43,7 +47,7 @@ function SourceBadges({ sources }: { sources: ChatSource[] }) {
   )
 }
 
-export default function ChatPanel({ taskId }: ChatPanelProps) {
+export default function ChatPanel({ taskId, mode, onModeChange }: ChatPanelProps) {
   const [input, setInput] = useState('')
   const [loading, setLoading] = useState(false)
   const [indexStatus, setIndexStatus] = useState<IndexStatus | null>(null)
@@ -218,16 +222,31 @@ export default function ChatPanel({ taskId }: ChatPanelProps) {
       {/* 头部 */}
       <div className="flex items-center justify-between border-b px-3 py-2">
         <span className="text-sm font-medium">AI 问答</span>
-        {messages.length > 0 && (
+        <div className="flex items-center gap-1">
           <Button
             variant="ghost"
             size="sm"
-            className="h-7 px-2 text-neutral-400 hover:text-red-500"
-            onClick={() => clearChat(taskId)}
+            className="h-7 px-2 text-neutral-400 hover:text-neutral-600"
+            onClick={() => onModeChange(mode === 'half' ? 'full' : 'half')}
+            title={mode === 'half' ? '全屏' : '半屏'}
           >
-            <Trash2 className="h-3.5 w-3.5" />
+            {mode === 'half' ? (
+              <Maximize2 className="h-3.5 w-3.5" />
+            ) : (
+              <Minimize2 className="h-3.5 w-3.5" />
+            )}
           </Button>
-        )}
+          {messages.length > 0 && (
+            <Button
+              variant="ghost"
+              size="sm"
+              className="h-7 px-2 text-neutral-400 hover:text-red-500"
+              onClick={() => clearChat(taskId)}
+            >
+              <Trash2 className="h-3.5 w-3.5" />
+            </Button>
+          )}
+        </div>
       </div>
 
       {/* 消息列表 */}

BillNote_frontend/src/pages/HomePage/components/MarkdownHeader.tsx

@@ -1,7 +1,7 @@
 'use client'
 
 import { useEffect, useState } from 'react'
-import { Copy, Download, BrainCircuit, MessageSquare, PanelRight, Maximize2 } from 'lucide-react'
+import { Copy, Download, BrainCircuit, MessageSquare } from 'lucide-react'
 import { Button } from '@/components/ui/button'
 import { Select, SelectContent, SelectItem, SelectTrigger } from '@/components/ui/select'
 import { Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from '@/components/ui/tooltip'
@@ -188,40 +188,22 @@ export function MarkdownHeader({
           </Tooltip>
         </TooltipProvider>
         {setShowChat && (
-          <div className="flex items-center gap-0.5 ml-1">
-            <TooltipProvider>
-              <Tooltip>
-                <TooltipTrigger asChild>
-                  <Button
-                    onClick={() => setShowChat(showChat === 'half' ? false : 'half')}
-                    variant={showChat === 'half' ? 'default' : 'ghost'}
-                    size="sm"
-                    className="h-8 px-2"
-                  >
-                    <PanelRight className="mr-1.5 h-4 w-4" />
-                    <span className="text-sm">问答</span>
-                  </Button>
-                </TooltipTrigger>
-                <TooltipContent>侧边问答（半屏）</TooltipContent>
-              </Tooltip>
-            </TooltipProvider>
-            <TooltipProvider>
-              <Tooltip>
-                <TooltipTrigger asChild>
-                  <Button
-                    onClick={() => setShowChat(showChat === 'full' ? false : 'full')}
-                    variant={showChat === 'full' ? 'default' : 'ghost'}
-                    size="sm"
-                    className="h-8 px-2"
-                  >
-                    <Maximize2 className="mr-1.5 h-4 w-4" />
-                    <span className="text-sm">全屏问答</span>
-                  </Button>
-                </TooltipTrigger>
-                <TooltipContent>全屏问答</TooltipContent>
-              </Tooltip>
-            </TooltipProvider>
-          </div>
+          <TooltipProvider>
+            <Tooltip>
+              <TooltipTrigger asChild>
+                <Button
+                  onClick={() => setShowChat(showChat ? false : 'half')}
+                  variant={showChat ? 'default' : 'ghost'}
+                  size="sm"
+                  className="h-8 px-2"
+                >
+                  <MessageSquare className="mr-1.5 h-4 w-4" />
+                  <span className="text-sm">AI 问答</span>
+                </Button>
+              </TooltipTrigger>
+              <TooltipContent>基于笔记内容的 AI 问答</TooltipContent>
+            </Tooltip>
+          </TooltipProvider>
         )}
       </div>
     </div>

BillNote_frontend/src/pages/HomePage/components/MarkdownViewer.tsx

@@ -221,10 +221,9 @@ const MarkdownViewer: FC<MarkdownViewerProps> = ({ status }) => {
         <div className="flex flex-1 overflow-hidden bg-white py-2">
           {selectedContent && selectedContent !== 'loading' && selectedContent !== 'empty' ? (
             <>
-              {/* 全屏问答模式：隐藏 markdown，ChatPanel 占满 */}
               {showChat === 'full' && currentTask ? (
                 <div className="h-full w-full">
-                  <ChatPanel taskId={currentTask.id} />
+                  <ChatPanel taskId={currentTask.id} mode="full" onModeChange={setShowChat} />
                 </div>
               ) : (
               <>
@@ -486,7 +485,7 @@ const MarkdownViewer: FC<MarkdownViewerProps> = ({ status }) => {
               {/* 侧边问答模式：markdown + ChatPanel 各占一半 */}
               {showChat === 'half' && currentTask && (
                 <div className="ml-2 h-full w-1/2 shrink-0">
-                  <ChatPanel taskId={currentTask.id} />
+                  <ChatPanel taskId={currentTask.id} mode="half" onModeChange={setShowChat} />
                 </div>
               )}
               </>