feat: add Zod validation for auth endpoints

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -29,7 +29,8 @@
         "react-datepicker": "^9.1.0",
         "react-dom": "^18.3.1",
         "react-quill-new": "^3.8.3",
-        "react-router-dom": "^6.30.3"
+        "react-router-dom": "^6.30.3",
+        "zod": "^4.3.6"
       },
       "devDependencies": {
         "@types/bcryptjs": "^2.4.6",
@@ -3748,6 +3749,15 @@
       "engines": {
         "node": ">=12"
       }
+    },
+    "node_modules/zod": {
+      "version": "4.3.6",
+      "resolved": "https://registry.npmjs.org/zod/-/zod-4.3.6.tgz",
+      "integrity": "sha512-rftlrkhHZOcjDwkGlnUtZZkvaPHCsDATp4pGpuOOMDaTdDDXF91wuVDJoWoPsKX/3YPQ5fHuF3STjcYyKr+Qhg==",
+      "license": "MIT",
+      "funding": {
+        "url": "https://github.com/sponsors/colinhacks"
+      }
     }
   }
 }