chore: Update package-lock.json with next-themes dependency

npm install was run to sync package-lock.json with the updated
package.json that includes next-themes for dark theme support.

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

e-voting-system/frontend/package-lock.json

@@ -15,6 +15,7 @@
         "clsx": "^2.0.0",
         "lucide-react": "^0.344.0",
         "next": "^15.0.0",
+        "next-themes": "^0.2.1",
         "react": "^18.3.1",
         "react-dom": "^18.3.1",
         "react-hook-form": "^7.66.0",
@@ -4641,6 +4642,17 @@
         }
       }
     },
+    "node_modules/next-themes": {
+      "version": "0.2.1",
+      "resolved": "https://registry.npmjs.org/next-themes/-/next-themes-0.2.1.tgz",
+      "integrity": "sha512-B+AKNfYNIzh0vqQQKqQItTS8evEouKD7H5Hj3kmuPERwddR2TxvDSFZuTj6T7Jfn1oyeUyJMydPl1Bkxkh0W7A==",
+      "license": "MIT",
+      "peerDependencies": {
+        "next": "*",
+        "react": "*",
+        "react-dom": "*"
+      }
+    },
     "node_modules/next/node_modules/postcss": {
       "version": "8.4.31",
       "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.4.31.tgz",