fix validation and 500 bugs

backend/src/main/java/com/petshop/backend/controller/ChatController.java

@@ -7,6 +7,7 @@ import com.petshop.backend.dto.chat.MessageResponse;
 import com.petshop.backend.dto.chat.UpdateConversationRequest;
 import com.petshop.backend.entity.Message;
 import com.petshop.backend.entity.User;
+import com.petshop.backend.exception.ResourceNotFoundException;
 import com.petshop.backend.repository.MessageRepository;
 import com.petshop.backend.repository.UserRepository;
 import com.petshop.backend.service.ChatAttachmentStorageService;
@@ -115,7 +116,7 @@ public class ChatController {
     public ResponseEntity<Resource> getMessageAttachment(@PathVariable Long messageId) {
         User user = getCurrentUser();
         Message message = messageRepository.findById(messageId)
-                .orElseThrow(() -> new RuntimeException("Message not found"));
+                .orElseThrow(() -> new ResourceNotFoundException("Message not found with id: " + messageId));
 
         if (!chatService.hasConversationAccess(message.getConversationId(), user.getId(), user.getRole())) {
             throw new AccessDeniedException("Access denied to this message attachment");

backend/src/main/java/com/petshop/backend/dto/appointment/AppointmentRequest.java

@@ -1,5 +1,6 @@
 package com.petshop.backend.dto.appointment;
 
+import jakarta.validation.constraints.NotBlank;
 import jakarta.validation.constraints.NotNull;
 import java.time.LocalDate;
 import java.time.LocalTime;
@@ -21,7 +22,7 @@ public class AppointmentRequest {
     @NotNull(message = "Appointment time is required")
     private LocalTime appointmentTime;
 
-    @NotNull(message = "Appointment status is required")
+    @NotBlank(message = "Appointment status is required")
     private String appointmentStatus;
 
     private Long petId;

backend/src/main/java/com/petshop/backend/dto/service/ServiceRequest.java

@@ -18,6 +18,7 @@ public class ServiceRequest {
     @Positive(message = "Price must be positive")
     private BigDecimal servicePrice;
 
+    @NotNull(message = "Service duration is required")
     @Positive(message = "Duration must be positive")
     private Integer serviceDuration;