Pin the canvas height to what is actually visible, and three fixes

Viewport, again — the homescreen app was the case that broke it. Watching for a
signal cannot work there: launched standalone, iOS resolves the CSS viewport once
against a provisional box and never re-resolves it, so no resize, no layout
change, nothing for a ResizeObserver to observe. Only a rotation forced the issue.
So the CSS box is now a proposal: visualViewport says what is really visible and
the height gets pinned in px to match, re-read on every fit — plus a short settle
salvo after launch, since that launch announces nothing.

- The countdown skipped the transition, where overT is parked at 9999 to hold the
  point flow. It read as RESUMING IN 9999 after the first game you ever win.
- Countdown moved off the HUD line into the open, at a readable size.
- A returned shot is a glancing blow now, not a mirror. Reversing the incoming
  line sent every parry straight back up it — into the thrower — so a boss handed
  you a free wound per volley. Contact across the racket face sets the angle:
  dead centre still goes back at him, which is a placement you earn.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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