fix: Restore API Key prompt and fix unused imports

src/services/chatService.ts

@@ -142,8 +142,14 @@ export const chatService = {
   },
 
   async sendMessage(messages: Message[], onChunk: (content: string) => void, signal?: AbortSignal): Promise<void> {
-    const apiKey = this.getApiKey();
-    // Removed API Key prompt as requested
+    let apiKey = this.getApiKey();
+    if (!apiKey) {
+      const input = prompt('Please enter your SiliconFlow API Key:');
+      if (input) {
+        this.setApiKey(input);
+        apiKey = input;
+      }
+    }
     
     try {
       const response = await fetch(API_URL, {