feat: implement authentication system for API Gateway and FileService

- Add JWT Bearer token validation to API Gateway with restricted CORS
- Add cookie-based JWT validation to FileService for browser image requests
- Create shared authentication infrastructure in FictionArchive.Service.Shared
- Update frontend to set fa_session cookie after OIDC login
- Add [Authorize] attributes to GraphQL mutations with role-based restrictions
- Configure OIDC settings for both services in docker-compose

Implements FA-17: Authentication for microservices architecture

FictionArchive.Service.FileService/Controllers/S3ProxyController.cs

@@ -2,6 +2,7 @@ using System.Web;
 using Amazon.S3;
 using Amazon.S3.Model;
 using FictionArchive.Service.FileService.Models;
+using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Options;
@@ -10,6 +11,7 @@ namespace FictionArchive.Service.FileService.Controllers
 {
     [Route("api/{*path}")]
     [ApiController]
+    [Authorize]
     public class S3ProxyController : ControllerBase
     {
         private readonly AmazonS3Client _amazonS3Client;