initialize
Warms up the hidden WebView and loads bridge.html.
This is an optional optimization - if not called, the first highlightToHtml or highlight call will initialize automatically. Call this early (e.g. on screen entry) to reduce latency on the first highlight request.
Safe to call multiple times - idempotent.
Return
Result.success when the WebView load has been started (full readiness is signalled asynchronously via isInitialized), or Result.failure wrapping a HighlightException.WebViewInitFailed if initialization fails.