Introduces a public App/TextBox builder API that renders word-wrapped
ASCII text in taffy-laid-out rectangles via a wgpu GPU pipeline.
- App/TextBox builder API (width, height, font_size, text_color, background, padding)
- Taffy flex-column layout tree computed per frame
- cosmic-text shapes and rasterizes text to a CPU RGBA8 buffer each frame
- Two wgpu pipelines: rect (colored quads) and text (textured quads)
- Winit event loop wired through ApplicationHandler