tauri-runtime-servocat 1.5.0

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. v1.5.0 plumbs `PendingWebview::ipc_handler` so a Tauri app's `tauri::Builder::invoke_handler` is stored alongside the webview and can be fired through the inherent `ServocatWebviewDispatch::send_ipc(request)` method (the Rust-side half of the JS<->host IPC bridge). This closes the committed 1.x roadmap; subsequent 1.x patch releases will wire the JS-side `__TAURI_INTERNALS__.postMessage` bridge through to the same handler. The Servo no-AI policy disqualifies upstream contribution; this is the AI-built parallel.