Stop the dead for the changeover instead of letting the player wander

Oliver vetoed the free movement between points on sight: he never walks
freely during play, so being able to only between points reads as the game
breaking, not as a fix. Reverted to 'rally' only, and the rule is written into
the settled-feel list so it doesn't get re-invented.

The frozen changeover is answered his other way instead — the dead wait too.
`held` in updateZombies stops their advance, their steering and the eat check
for the breather; they still bleed and burn, they just stand there, because
the umpire called time and it is still a tennis match. The path where this
actually bit: losing a duel scheduled on a changeover beat spawns five fresh
shamblers and THEN starts five seconds you have no agency in.

The stuck pose was never about movement — 'run' is the one pose expirePose
doesn't expire, and runT stops advancing outside the block, so a beat that
began mid-stride welded him to a single frame. Reset it and it's fixed for
every phase.

And he could walk off the screen in ordinary play, not just during the beat I
had added: P_BOUNDS.x is 6.5 m, portrait shows about ±4 m at the baseline.
The xVis clamp already existed but only applied during auto-fire; it now
always applies, floored at the sideline so every legal ball stays catchable.

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

index.html

@@ -60,6 +60,6 @@
     <p class="start">TAP TO START</p>
   </div>
 </div>
-<script type="module" src="main.js?v=36"></script>
+<script type="module" src="main.js?v=37"></script>
 </body>
 </html>