[F] Fix error reporting

src/main/java/icu/samnyan/aqua/net/utils/ErrorResponse.kt

@@ -0,0 +1,17 @@
+package icu.samnyan.aqua.net.utils
+
+import ext.Str
+import org.springframework.http.ResponseEntity
+import org.springframework.web.bind.annotation.ControllerAdvice
+import org.springframework.web.bind.annotation.ExceptionHandler
+
+class ApiException(val code: Int, message: Str) : RuntimeException(message)
+
+@ControllerAdvice
+class GlobalExceptionHandler {
+    @ExceptionHandler(ApiException::class)
+    fun handleCustomApiException(e: ApiException): ResponseEntity<Any?> {
+        // On error, return the error code and message
+        return ResponseEntity.status(e.code).body(e.message)
+    }
+}