feat(web): 将原生 select 替换为 shadcn/ui Select 组件并支持图片消息发送

- 在 AccountForm、AssetGallery、ChatView、ConfigForm、PromptEditor 中将 `<select>` 替换为 shadcn/ui 的 Select 组件以统一 UI 风格
- 在 ChatView 和 useChat hook 中支持发送图片附件
- 更新 pi-bridge 和 ws/chat 以处理 agent 调用中的图片数据

web/client/src/components/chat/ChatView.tsx

@@ -126,10 +126,10 @@ export function ChatView() {
     creatingRef.current = false;
   }, [createConversation, selectedAccountId]);
 
-  const handleSend = useCallback((content: string) => {
+  const handleSend = useCallback((content: string, images?: Array<{ data: string; mimeType: string }>) => {
     if (quote) { content = `> ${quote}\n\n${content}`; setQuote(null); }
     if (conversationId) {
-      send(content);
+      send(content, images);
     } else {
       handleSendNew(content);
     }
@@ -154,14 +154,18 @@ export function ChatView() {
           {accounts.length > 0 && (
             <div className="flex items-center gap-2 mt-3 justify-center">
               <span className="text-xs text-zinc-400">当前账号:</span>
-              <select
+              <Select
                 value={selectedAccountId || ''}
-                onChange={(e) => useAppStore.getState().setSelectedAccountId(e.target.value || null)}
-                className="h-7 rounded-lg border border-zinc-100 bg-white px-2.5 text-xs text-zinc-600 hover:border-zinc-200 transition-colors"
+                onValueChange={(v) => useAppStore.getState().setSelectedAccountId(v === 'none' ? null : v)}
               >
-                <option value="">不指定</option>
-                {accounts.map((a) => <option key={a.id} value={a.id}>{a.name}</option>)}
-              </select>
+                <SelectTrigger className="h-7 w-auto min-w-[100px] text-xs px-2.5 border-zinc-100 hover:border-zinc-200">
+                  <SelectValue placeholder="不指定" />
+                </SelectTrigger>
+                <SelectContent>
+                  <SelectItem value="none">不指定</SelectItem>
+                  {accounts.map((a) => <SelectItem key={a.id} value={a.id}>{a.name}</SelectItem>)}
+                </SelectContent>
+              </Select>
             </div>
           )}
           {recentConvs.length > 0 && (