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.API/FictionArchive.API.csproj

@@ -20,6 +20,7 @@
         <PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="9.0.11" />
         <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="8.0.7" />
         <PackageReference Include="Swashbuckle.AspNetCore" Version="6.6.2"/>
+        <PackageReference Include="Microsoft.AspNetCore.Authentication.JwtBearer" Version="8.0.11" />
     </ItemGroup>
     
     <!-- Builds the Fusion graph file before building the application itself (skipped in CI) -->