fix: backgammon gameplay — working buttons, correct canvas rendering, no DPR bugs

- Remove DPR ctx.scale() that compounded every frame and broke all rendering
- Use logical pixel dimensions directly (canvas.width = logical size)
- Fix isSel/isValid closures that caused undefined reference errors in checker glow
- Simplify game scene: roll button is now a normal element in .bgg-controls (not overlay)
- Event handlers correctly scale click coords via rect ratio
- Remove unused getCheckerScreenPos import from move-animator
- All buttons (roll, double, emote, quit) bind via addEventListener properly
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/js/modules/backgammon/canvas/board-renderer.js

@@ -150,13 +150,15 @@ export function drawBoard(ctx, w, h, state, options = {}) {
     const vis = Math.min(count, maxVis);
     const spacing = Math.min(checkerR * 2, pointH / vis);
 
+    const pointIsSelected = selectedPoint === i;
+    const pointIsValid = highlights.includes(i);
+
     for (let j = 0; j < vis; j++) {
       const cy = isTop ? y + checkerR + j * spacing : y - checkerR - j * spacing;
       const isTopChecker = j === vis - 1;
-      const glowing = isTopChecker && isSel === i;
       drawChecker(ctx, cx, cy, pieces[j].type, checkerR, {
-        glow: isSel && isTopChecker,
-        pulse: isValid(i) && isTopChecker
+        glow: pointIsSelected && isTopChecker,
+        pulse: pointIsValid && isTopChecker
       });
     }
     if (count > maxVis) {
@@ -194,9 +196,6 @@ export function drawBoard(ctx, w, h, state, options = {}) {
   // ── Particles ──
   if (particles.length) drawParticles(ctx, particles);
 
-  function isValid(idx) { return highlights.includes(idx); }
-  function isSel(idx) { return selectedPoint === idx; }
-
   return layout;
 }
 

public/js/modules/backgammon/canvas/move-animator.js

 // Arc-based move animator with overshoot bounce + particle burst
-import { getPointCoords, getCheckerScreenPos } from './board-renderer.js';
+import { getPointCoords } from './board-renderer.js';
 
 const MOVE_DURATION = 320;
 const HIT_DURATION = 420;