feat: Enhance User model with URL validation and documentation

backend/models/User.js

@@ -1,6 +1,19 @@
 const mongoose = require('mongoose');
 const Schema = mongoose.Schema;
 
+/**
+ * User Schema
+ * @typedef {Object} User
+ * @property {string} googleId - Google OAuth ID (optional)
+ * @property {string} name - User's full name
+ * @property {string} email - User's email address
+ * @property {boolean} isEmailVerified - Email verification status
+ * @property {string} password - Hashed password (required if no googleId)
+ * @property {string} avatar - Path to user's avatar image
+ * @property {string} bio - User's biography
+ * @property {string[]} skills - Array of user's skills
+ * @property {Object} socialLinks - User's social media profiles
+ */
 const UserSchema = new Schema({
    googleId: {
     type: String,
@@ -32,25 +45,104 @@ const UserSchema = new Schema({
     default: '/uploads/avatars/default-avatar.png'
   },
   bio: {
-    type: String
+    type: String,
+    maxlength: [500, 'Bio cannot be more than 500 characters']
   },
   location: {
     type: String
   },
   skills: {
-    type: [String]
+    type: [String],
+    validate: {
+      validator: function(v) {
+        return v.length <= 20; // Maximum 20 skills
+      },
+      message: 'Cannot have more than 20 skills'
+    }
   },
   socialLinks: {
-    github: String,
-    gitlab: String,
-    linkedin: String,
-    twitter: String,
+    github: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/github\.com\/[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid GitHub URL format'
+      }
+    },
+    gitlab: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/gitlab\.com\/[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid GitLab URL format'
+      }
+    },
+    linkedin: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/(?:www\.)?linkedin\.com\/in\/[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid LinkedIn URL format'
+      }
+    },
+    twitter: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/(?:www\.)?twitter\.com\/[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid Twitter URL format'
+      }
+    },
     website: String,
-    codechef: String,
-    hackerrank: String,
-    leetcode: String,
-    codeforces: String,
-    hackerearth: String
+    codechef: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/www\.codechef\.com\/users\/[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid CodeChef URL format'
+      }
+    },
+    hackerrank: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/www\.hackerrank\.com\/[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid HackerRank URL format'
+      }
+    },
+    leetcode: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/leetcode\.com\/[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid LeetCode URL format'
+      }
+    },
+    codeforces: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/codeforces\.com\/profile\/[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid Codeforces URL format'
+      }
+    },
+    hackerearth: {
+      type: String,
+      validate: {
+        validator: function(v) {
+          return !v || /^https:\/\/www\.hackerearth\.com\/@[\w-]+\/?$/.test(v);
+        },
+        message: 'Invalid HackerEarth URL format'
+      }
+    }
   },
   projects: [
     {