disk: simplify HUD hitbox to match label buffer + quiet debug overlay
Replace the ad-hoc width/height calculation (visible text width + descender
padding, right padding, clamped y, x=0 start) with a direct mapping to the
rendered HUD label buffer. The hitbox now sits at finalX/finalY with width
and height from hudAnimationState.labelWidth/labelHeight (with existing
fallbacks), which is how the overlay is actually drawn — so the hitbox and
the visible area stay aligned as the HUD animates.
Also tidy the debug overlay:
- Make it opt-in (globalThis.debugHudHitbox) instead of default-on.
- Swap the magenta fill for a blinking green double outline that doesn't
obscure piece content while inspecting.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>