fix(physics): restore four-sided board bounds

Finish a ball before record scanning when its clamped prediction leaves x=(0,340000] or y=(0,460000], and remove only the escaping slot during multiball. Delete the invented post-move y>470 shortcut so collision responses that land outside persist until the original next-substep check.

Test Plan:
- cargo test --all-targets
- cargo clippy --all-targets --all-features -- -D warnings
- rumdl check CHANGELOG.md RECONSTRUCTION.md README.md
- git diff --check

tdkpin-rs/CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to
 
 ### Fixed
 
+- Replace the invented post-move `y>470` fallback with the original pre-scan
+  prediction bounds `x<=0 || x>340000 || y<=0 || y>460000`, including
+  one-slot removal during multiball and next-substep handling after a response.
 - Remove the invented 180 ms whole-frame nudge shake; original nudges affect
   ball-slot velocities, sound, and Tilt state without moving the viewport.
 - Match `SndPlaySound(SND_ASYNC|SND_NODEFAULT)` playback: stop the previous WAV