M3: console.log -> Logger + UI redesign (QuestionBank) + S7/A9/A10/A11/U11 bug fixes + #1/#2/#3/#4 enhancements + i18n for QuestionBank pages

server/src/api/api.service.ts

@@ -1,10 +1,12 @@
-import { Injectable } from '@nestjs/common';
+import { Injectable, Logger } from '@nestjs/common';
 import { ChatOpenAI } from '@langchain/openai';
 import { ModelConfig } from '../types';
 import { I18nService } from '../i18n/i18n.service';
 
 @Injectable()
 export class ApiService {
+  private readonly logger = new Logger(ApiService.name);
+
   constructor(private i18nService: I18nService) {}
 
   // Simple health check method
@@ -23,7 +25,7 @@ export class ApiService {
       const response = await llm.invoke(prompt);
       return response.content.toString();
     } catch (error) {
-      console.error('LangChain call failed:', error);
+      this.logger.error('LangChain call failed:', error);
       if (error.message?.includes('401')) {
         throw new Error(this.i18nService.getMessage('invalidApiKey'));
       }