The @if/@else toggle between the contentEditable surface and the code
textarea broke the static ViewChild('surface') query: Angular never
resolves a static query for an element inside a conditional block, so
surface stayed undefined and every keystroke threw in emitChange().
Render both elements always and toggle visibility with [hidden]
instead, and add an ngAfterViewInit sync as a safety net for the
initial html input on the first change-detection pass.
