🛡️ feat: Add Middleware for JSON Parsing and Prompt Group Updates (#10757)

* 🗨️ fix: Safe Validation for Prompt Updates

- Added `safeValidatePromptGroupUpdate` function to validate and sanitize prompt group update requests, ensuring only allowed fields are processed and sensitive fields are stripped.
- Updated the `patchPromptGroup` route to utilize the new validation function, returning appropriate error messages for invalid requests.
- Introduced comprehensive tests for the validation logic, covering various scenarios including allowed and disallowed fields, enhancing overall request integrity and security.
- Created a new schema file for prompt group updates, defining validation rules and types for better maintainability.

* 🔒 feat: Add JSON parse error handling middleware

packages/api/src/middleware/json.ts

@@ -0,0 +1,40 @@
+import { logger } from '@librechat/data-schemas';
+import type { Request, Response, NextFunction } from 'express';
+
+/**
+ * Middleware to handle JSON parsing errors from express.json()
+ * Prevents user input from being reflected in error messages (XSS prevention)
+ *
+ * This middleware should be placed immediately after express.json() middleware.
+ *
+ * @param err - Error object from express.json()
+ * @param req - Express request object
+ * @param res - Express response object
+ * @param next - Express next function
+ *
+ * @example
+ * app.use(express.json({ limit: '3mb' }));
+ * app.use(handleJsonParseError);
+ */
+export function handleJsonParseError(
+  err: Error & { status?: number; body?: unknown },
+  req: Request,
+  res: Response,
+  next: NextFunction,
+): void {
+  if (err instanceof SyntaxError && err.status === 400 && 'body' in err) {
+    logger.warn('[JSON Parse Error] Invalid JSON received', {
+      path: req.path,
+      method: req.method,
+      ip: req.ip,
+    });
+
+    res.status(400).json({
+      error: 'Invalid JSON format',
+      message: 'The request body contains malformed JSON',
+    });
+    return;
+  }
+
+  next(err);
+}