feat: implement QuestionBank CRUD with pagination and template query

- Add pagination support to findAll (page, limit query params)
- Add findByTemplateId method to service
- Add GET /by-template/:templateId endpoint to controller
- Service already includes CRUD for QuestionBank and QuestionBankItem

server/src/common/json-utils.ts

@@ -0,0 +1,48 @@
+/**
+ * Safely parses JSON from a string, handling markdown code blocks and leading/trailing text.
+ */
+export function safeParseJson<T = any>(text: string): T | null {
+  if (!text) return null;
+
+  let jsonStr = text.trim();
+
+  // 1. Try to extract JSON from markdown code blocks if they exist
+  // Matches ```json ... ``` or just ``` ... ```
+  const codeBlockRegex = /```(?:json)?\s*([\s\S]*?)\s*```/i;
+  const match = jsonStr.match(codeBlockRegex);
+
+  if (match && match[1]) {
+    jsonStr = match[1].trim();
+  } else {
+    // 2. If no markdown block, try to find the start and end of JSON characters
+    // This handles cases where the AI adds introductory or concluding text outside the block
+    const firstOpenBrace = jsonStr.indexOf('{');
+    const firstOpenBracket = jsonStr.indexOf('[');
+    
+    let startIndex = -1;
+    if (firstOpenBrace !== -1 && (firstOpenBracket === -1 || firstOpenBrace < firstOpenBracket)) {
+      startIndex = firstOpenBrace;
+    } else if (firstOpenBracket !== -1) {
+      startIndex = firstOpenBracket;
+    }
+
+    if (startIndex !== -1) {
+      const lastCloseBrace = jsonStr.lastIndexOf('}');
+      const lastCloseBracket = jsonStr.lastIndexOf(']');
+      const endIndex = Math.max(lastCloseBrace, lastCloseBracket);
+      
+      if (endIndex !== -1 && endIndex > startIndex) {
+        jsonStr = jsonStr.substring(startIndex, endIndex + 1);
+      }
+    }
+  }
+
+  try {
+    return JSON.parse(jsonStr) as T;
+  } catch (error) {
+    console.error('[safeParseJson] Failed to parse JSON:', error);
+    console.error('[safeParseJson] Original text:', text);
+    console.error('[safeParseJson] Extracted string:', jsonStr);
+    return null;
+  }
+}