Add JWT auth for protected routes, add /reg endpoint, remove /user endpoints

bin/middleware/auth_middleware.dart

@@ -0,0 +1,29 @@
+import 'package:shelf/shelf.dart';
+import 'package:dart_jsonwebtoken/dart_jsonwebtoken.dart';
+import 'package:dotenv/dotenv.dart';
+
+class AuthMiddleware {
+  final Handler handler;
+  
+  AuthMiddleware(this.handler);
+  
+  Future<Response> call(Request request) async {
+    final authorization = request.headers['authorization'];
+    
+    if (authorization == null || !authorization.startsWith('Bearer ')) {
+      return Response(401, body: 'Authorization header missing or invalid');
+    }
+    
+    final token = authorization.substring(7);
+    
+    try {
+      final dotenv = DotEnv();
+      final secret = dotenv['JWT_SECRET'] ?? '';
+      final decoded = JWT.verify(token, SecretKey(secret));
+      
+      return handler(request);
+    } catch (e) {
+      return Response(401, body: 'Invalid or expired token');
+    }
+  }
+}