feat: HD Remaster toggle with 4x canvas render path

G.hdRemaster persisted in localStorage (meatslicer_hd_remaster), toggled
from the title screen via H key or the bottom-left tag; activation reloads
so the asset tier and canvas resolution swap at boot. draw() applies a
uniform hdScale() transform, the room-layer cache renders at render scale,
and image smoothing follows the tier.

js/state.js

@@ -49,6 +49,7 @@ const G = {
   sfxVol: 0.45,
   musicVol: 0.55,
   hudAlpha: 1,
+  hdRemaster: false,
   imagesLoaded: false,
   roomLayer: null,
   roomLayerKey: '',
@@ -70,6 +71,8 @@ const PRESSURE_DROP_BASE = 3;        // dial 0 == 0.03 relief base
 const DEATH_LOCK = 3;
 const PRESSURE_DIAL_MIN = -10, PRESSURE_DIAL_MAX = 10;
 
+function hdScale() { return G.hdRemaster ? 4 : 1; }
+
 // Preserve the old -5 / 0 / +5 balance while adding genuinely wider extremes.
 function pressureGainUnits(dial) {
   const d = clamp(dial, PRESSURE_DIAL_MIN, PRESSURE_DIAL_MAX);