Servo-replacement runtime for Tauri: wires html-cat, css-cat, dom-cat, layout-cat, paint-cat, net-cat, boa-cat, ecma-runtime-cat, and web-api-cat into a single rendering + scripting pipeline. v0.4.0 adds a winit + softbuffer window and a runnable demo binary so the rasterized output can be shown on-screen. IPC bridge and tauri_runtime::Runtime trait impl are committed-to deliverables for subsequent versions. The Servo no-AI policy disqualifies upstream contribution; this is the AI-built parallel.