feat(drum_highway_3d): foundation for guitar-highway visual parity (D1) (#695)

- Consume host adaptive-quality bundle.renderScale; fold into DPR like
  highway_3d (splitscreen proxy: >1 instance caps baseDPR at 1.25)
- Bloom: port _bloomEnsure/_bloomDispose (UnrealBloomPass 0.65/0.5/0.82,
  MSAA HalfFloat target, ACES<->None tone-mapping switch); rebuilt across
  the kit-change renderer recreation; direct render is the degrade path
- FX settings scaffold: FX_DEFAULTS + readFxSettings + drumH3dSetFx
  (drum_h3d_bg_* keys), Graphics section in settings.html (bloom toggle,
  default ON, live-applies)
- _applyLaneFlashes dead-code comment updated (visual consumer lands in
  the hit-FX PR)
- __test export + tests/data_layer.test.js (vm harness, 8 tests) —
  picked up by the CI glob from the bundling PR; README refreshed

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

plugins/drum_highway_3d/settings.html

@@ -42,6 +42,20 @@
         <p class="text-xs text-gray-500 mt-1">0 = down the lanes · 1 = top-down</p>
     </div>
 
+    <!-- Graphics -->
+    <div class="mt-6 border-t border-gray-800 pt-4">
+        <h4 class="text-xs font-medium text-gray-300 mb-2">Graphics</h4>
+        <label for="drumh3d-fx-bloom" class="flex items-center gap-2 text-xs text-gray-300 cursor-pointer">
+            <input type="checkbox" id="drumh3d-fx-bloom" checked
+                onchange="window.drumH3dSetFx && window.drumH3dSetFx('bloom', this.checked)">
+            Glow (bloom)
+        </label>
+        <p class="text-xs text-gray-500 mt-1">
+            Soft light-bleed around the hit line and bright notes. Applies
+            live; turn off to reclaim GPU headroom on weak machines.
+        </p>
+    </div>
+
     <!-- MIDI input -->
     <div class="mt-6 border-t border-gray-800 pt-4">
         <h4 class="text-xs font-medium text-gray-300 mb-2">MIDI input</h4>
@@ -422,6 +436,16 @@
                 cam.value = String(c);
                 camVal.textContent = c.toFixed(2);
             }
+
+            // FX toggles (drum_h3d_bg_* — guitar-parity graphics controls).
+            // Only explicit values override; absent/corrupt keys keep the
+            // default (ON), matching screen.js readFxSettings.
+            const storedBloom = localStorage.getItem('drum_h3d_bg_bloom');
+            if (storedBloom === '1' || storedBloom === 'true') {
+                document.getElementById('drumh3d-fx-bloom').checked = true;
+            } else if (storedBloom === '0' || storedBloom === 'false') {
+                document.getElementById('drumh3d-fx-bloom').checked = false;
+            }
         } catch (e) {
             console.warn('[Drum-Hwy3D settings] hydration failed:', e);
         }