fix(webview): route non http(s) schemes out of WebPageView

[jim-daf]

Closes #12.

WebPageView's WebViewClient overrides shouldInterceptRequest, doUpdateVisitedHistory, onPageStarted and onPageFinished, but not shouldOverrideUrlLoading. Any navigation the loaded supplier page hands the WebView (a mailto: on a contact link, a tel: on a phone number, an intent: from a deep link) is dispatched by the default handler instead of leaving the in-app browser for the matching system app.

Change

Add a shouldOverrideUrlLoading override. Keep http, https and about: schemes inside the WebView, route the rest out via Intent.ACTION_VIEW, wrap the launch in try/catch (ActivityNotFoundException) so a missing handler does not crash the activity:

override fun shouldOverrideUrlLoading(view: WebView?, request: WebResourceRequest?): Boolean {
    val target = request?.url ?: return false
    val scheme = target.scheme?.lowercase()
    if (scheme == "http" || scheme == "https" || scheme == "about") return false
    return try {
        val intent = Intent(Intent.ACTION_VIEW, target).apply {
            addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
        }
        view?.context?.startActivity(intent)
        true
    } catch (e: ActivityNotFoundException) {
        Log.w("webview", "No handler for $target", e)
        true
    }
}

This sits alongside the existing WARNING comment on shouldInterceptRequest. The two hooks serve different roles (one for sub-resource requests, one for top-level navigations) so it does not replace the existing intercept logic.