Mock backend: the real API with the performance tests' fakes, for developing and testing the frontend without accounts or keys

The fakes move into Mediatracker.Testing; Program.cs becomes ApiHost with two hooks; Mediatracker.Api.Mock replaces the PDS, Tap, the metadata source and the login. Run configurations for Rider and WebStorm, and the Vite proxy target is configurable. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>


Author Erican Co-author Claude Sonnet 5.5 Date Commit Parent 0b8a06f0