Refactor entire backend

[danielchalmers]

This refactors Sentry Replay into a leaner Flyleaf-first WPF app structure while preserving the existing UI and workflows.

• removes the separate SentryReplay.Streaming project and the generic media-player abstraction
• moves playback coordination into SentryReplay/Playback with Flyleaf as the concrete runtime path
• moves main-window state and commands into MainWindowViewModel, leaving code-behind for WPF host layout and lifecycle plumbing
• reorganizes data models, services, converters, views, and tests into focused folders
• replaces noisy/skipped tests with a focused test suite covering data mapping, playback coordination, playlist/timeline behavior, converters, update parsing, and view-model state

The app keeps the current user interface and experience, but the codebase has fewer project boundaries, fewer unused abstractions, and clearer ownership for playback, UI state, services, and domain models.

This also fixes TeslaCam root discovery for app-local roots by checking both the working directory and AppContext.BaseDirectory.