fix: 修复画布聊天 ID 格式问题

从 canvas-{uuid} 格式中提取纯 UUID，以满足后端 schema 要求

Co-authored-by: Cursor <cursoragent@cursor.com>

components/canvas/CanvasChatPanel.tsx

@@ -153,15 +153,20 @@ export function CanvasChatPanel({ chatId, initialMessages = [], onClose, onOpenF
       api: "/api/chat",
       fetch: fetchWithErrorHandlers,
       prepareSendMessagesRequest(request) {
+        // 从 canvas-{uuid} 格式中提取纯 UUID，后端 schema 要求纯 UUID
+        const rawId = request.id.startsWith('canvas-') 
+          ? request.id.replace('canvas-', '') 
+          : request.id;
+        
         console.log("[CanvasChat] Preparing request:", {
-          id: request.id,
+          id: rawId,
           modelId: currentModelIdRef.current,
           imageParams: imageParamsRef.current,
           lastMessage: request.messages.at(-1),
         });
         return {
           body: {
-            id: request.id,
+            id: rawId,
             message: request.messages.at(-1),
             selectedChatModel: currentModelIdRef.current,
             selectedVisibilityType: "private",