feat: Refactor authentication and token management

- Updated EchoHubConnection to use ApiClient for token retrieval.
- Introduced ValidationConstants for common validation patterns and limits.
- Enhanced AuthDtos with refresh token support and expiration details.
- Added new ChatDtos for channel creation and topic updates.
- Created CommonDtos for error and paginated responses.
- Implemented RefreshToken model for managing refresh tokens.
- Modified JwtTokenService to generate and hash refresh tokens.
- Updated AuthController to handle registration, login, token refresh, and logout with improved error handling.
- Enhanced ChannelsController with channel creation, topic updates, and pagination for channel retrieval.
- Added FilesController for file management with rate limiting.
- Improved UsersController for profile updates and avatar uploads with validation.
- Integrated rate limiting across controllers to manage request load.
- Introduced FileValidationHelper for validating uploaded image files.
- Updated database context to include RefreshToken and enforce unique constraints.
- Enhanced ChatHub for improved channel and message handling with validation.
- Updated Program.cs to configure rate limiting and CORS policies.

src/EchoHub.Server/Controllers/FilesController.cs

@@ -1,19 +1,27 @@
+using EchoHub.Core.DTOs;
 using EchoHub.Server.Services;
+using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.RateLimiting;
 
 namespace EchoHub.Server.Controllers;
 
 [ApiController]
 [Route("api/files")]
+[Authorize]
+[EnableRateLimiting("general")]
 public class FilesController(FileStorageService fileStorage) : ControllerBase
 {
     [HttpGet("{fileId}")]
     public IActionResult GetFile(string fileId)
     {
+        if (!Guid.TryParse(fileId, out _))
+            return BadRequest(new ErrorResponse("Invalid file identifier."));
+
         var filePath = fileStorage.GetFilePath(fileId);
 
         if (filePath is null)
-            return NotFound(new { Error = "File not found." });
+            return NotFound(new ErrorResponse("File not found."));
 
         var contentType = Path.GetExtension(filePath).ToLowerInvariant() switch
         {