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.Shared/Models/Authentication/OidcConfiguration.cs

@@ -0,0 +1,12 @@
+namespace FictionArchive.Service.Shared.Models.Authentication;
+
+public class OidcConfiguration
+{
+    public string Authority { get; set; } = string.Empty;
+    public string ClientId { get; set; } = string.Empty;
+    public string Audience { get; set; } = string.Empty;
+    public bool ValidateIssuer { get; set; } = true;
+    public bool ValidateAudience { get; set; } = true;
+    public bool ValidateLifetime { get; set; } = true;
+    public bool ValidateIssuerSigningKey { get; set; } = true;
+}