fix(webview): route javascript: URLs through evaluateJavascript in the dispatcher

[jim-daf]

Closes #17.

GoJsActivity runs every script call into the EidoGo board through a single dispatcher (viewerq -> runOnUiThread -> wv.loadUrl(surl)). All the viewUrl("javascript:...") call sites end up there, so the actual WebView call is loadUrl("javascript:...") for every move state change. That's the legacy pattern: it adds a synthetic history entry on every script eval and cannot return a value to the caller.

There's already a long comment block in this file pointing at evaluateJavascript as the KitKat-era replacement. The swap at the dispatcher covers every existing call site without touching them individually:

if (surl != null && surl.startsWith("javascript:")) {
    GoJsActivity.main.wv.evaluateJavascript(
            surl.substring("javascript:".length()), null);
} else {
    GoJsActivity.main.wv.loadUrl(surl);
}

Non-javascript URLs still go through loadUrl exactly as before. The null callback keeps behaviour identical for the script branch since no existing call site reads a return value.