The control-surface guard added in the previous commit killed
double-tap-to-seek. The first tap pauses, which renders the full-screen
<button> play overlay over the video, so the SECOND tap lands on a
button — and the guard discarded it as "a tap on a control".
Mark that overlay `data-player-surface`: visually it IS the video, so it
must keep taking tap gestures despite being a <button>. The marker wins
over the interactive-tag check in isControlSurfaceTouch.
Adds VideoPlayer.tapSurface.test.ts, which renders the REAL component
and dispatches real touch/click events at whatever element is genuinely
on top. This is the gap that let four bugs ship in a row: the pure-unit
tests over registerTap/isControlSurfaceTouch/isSynthesizedTouchClick all
passed throughout, because each helper behaved exactly as specified —
every bug was in the composition, i.e. which element actually receives a
tap after Svelte re-renders. Modelling that DOM by hand in a test would
just re-encode the same wrong assumption, so these render it instead.
The new double-tap test was verified to fail with the fix reverted and
pass with it applied, in both directions.
