Move pure playback types into SentryReplay.Data

[danielchalmers]

What

Relocates the provider-agnostic playback types out of the WPF app project and into the existing SentryReplay.Data class library, so pure logic lives behind a compile-time boundary that cannot acquire WPF/Flyleaf dependencies.

Moved SentryReplay/Playback/ → SentryReplay.Data/Playback/:

• ClipTimeline.cs, ClipTimelinePosition.cs — pure timeline math (no usings)
• CameraPlayerEvents.cs — EventArgs wrappers (no usings)
• ICameraPlayer.cs — the playback abstraction seam (no usings)
• ClipPlaylist.cs — clip selection state; uses Serilog

Stayed in the app (SentryReplay/Playback/): FlyleafCameraPlayer.cs and VideoPlayerController.cs — both are genuinely Flyleaf/MVVM-coupled.

SentryReplay.Data.csproj: added <PackageReference Include="Serilog" Version="4.2.0" /> (matches the app's version) — required because ClipPlaylist logs via Serilog. Without it the move would not compile.

Why this is safe / cheap

• Namespace is flat SentryReplay; across both projects (no RootNamespace override), so the files compile unchanged after the move — no namespace, XAML, or test edits needed.
• The dependency graph is unchanged: the app already references SentryReplay.Data, so VideoPlayerController/FlyleafCameraPlayer still see ICameraPlayer and the pure types (app → Data). Tests already reference Data, so FakeCameraPlayer : ICameraPlayer still resolves.
• Files moved with git mv (tracked as renames, history preserved).

Verification

Full solution builds clean (0 warnings/errors); all 81 tests pass; dotnet format clean.

Notes

• Per the agreed plan, this deliberately does not rename Data → Domain (naming churn, no payoff) and does not create per-feature slice folders.
• Step 2 of the reorg. Remaining: rewrite AGENTS.md so the "preserve existing MVVM patterns" guidance no longer sanctions the old god-file pattern.