Add Deluge download client support

[blackax1]

Summary

Refactors and completes the Deluge download client implementation to align with the new download-client architecture boundaries introduced in PR #599, addressing PR #697.

Changes

Added

• DelugeRpcClient.cs to centralize HTTP JSON-RPC communications, session authentication, and daemon connectivity.
• DelugeConnectionTester.cs to encapsulate connection testing logic.
• DelugeAddWorkflow.cs to manage torrent submissions (magnets, files, URLs) and category labels.
• DelugeRemovalWorkflow.cs to handle torrent deletions.
• DelugeQueueFetchWorkflow.cs to manage queue monitoring and targeted polling with correct exception handling (DownloadClientAdapterPollingException).
• DelugeItemFetchWorkflow.cs to retrieve active download items.
• DelugeImportItemResolver.cs to resolve files and remote output paths before import.
• DelugeApiMock.cs to mock JSON-RPC responses.

Changed

• DownloadClientTypes.cs to define the "deluge" constant.
• DownloadClientRegistrationExtensions.cs to register the new Deluge workflows and adapter facade in dependency injection.
• DelugeAdapter.cs refactored as a thin adapter facade delegating to client-specific workflows.
• MockUtils.cs and ServiceCollectionBuilder.cs updated to register and configure DelugeApiMock for tests.
• DownloadClientWorkflowRegistrationTests.cs to verify Deluge workflows and adapter resolve correctly from DI.
• DelugeAdapterTests.cs rewritten to utilize the mock API registration pattern.

Testing

• Automated Tests: Verified that all backend unit and integration tests compile and pass successfully (dotnet test run within a .NET SDK 10.0 container, 1202/1202 passing).
• Manual Verification: Built the project locally as a container using the monorepo Dockerfile (podman build) and verified connectivity, queue updates, and configuration settings with a live Deluge instance.

[Algorant]

Oh cool thank you for doing this! Let me test it when I have some time.