Native winit window

The fifth chunk on the path to "first MP4 plays in the recorder via wisp". Builds a real OS window via [winit] 0.30 and hands the wgpu surface to wisp through [Application::from_wgpu].

What landed

• crates/preview/ — new crate with both a [lib] (pure helpers) and a [[bin]] (the winit app).
• Application::from_wgpu is the seam between embedding host (winit, in the future a winit child of Tauri) and wisp's Renderer.
• The window auto-sizes to the source video (clamped to a 640×360 minimum so it isn't comically small for tiny test fixtures).
• The sprite is centered and aspect_fit_scale-letterboxed against the current surface dimensions, so resizing the window keeps the video proportional.

Visual proof — render_offscreen example

The example rebuilds the same render path against an offscreen RenderTexture (no winit window required), so it runs in CI and produces a deterministic asset:

cargo run -p preview --example render_offscreen

Five frames into a 800×450 surface (16:9), with the 480×270 fixture letterboxed to fit.

What you're looking at. The committed sample.mp4 test fixture is a deterministic synthetic gradient (the M-DEC.1 mock-stream encoded once with x264 into an 11 KB MP4) — the visible "gradient look" is the fixture content, not a rendering bug. The chapter's claim is that the winit → wgpu → Application::from_wgpu → Player::tick → Renderer path delivers decoded frames into the surface; the horizontal-phase advance frame-to-frame is the proof. For a more representative example of decoded-video output, see the media chapters which use videotestsrc SMPTE colorbars.

Frame 00	Frame 01	Frame 02

Frame 03	Frame 04