feat(keys_highway_3d): foundation for guitar-highway visual parity (K1) (#696)

- setPixelRatio at last: DPR (cap 2; 1.25 when >1 instance) x host
  adaptive bundle.renderScale — HiDPI displays were rendering at CSS
  resolution and upscaling (soft/aliased)
- Bloom: port _bloomEnsure/_bloomDispose (UnrealBloomPass 0.65/0.5/0.82,
  MSAA HalfFloat target, ACES<->None switch); hit-line, flames and
  consume-glow benefit immediately; direct render is the degrade path
- First settings panel: settings.html (graphics category) with a live
  Glow (bloom) toggle; FX scaffold (FX_DEFAULTS/readFxSettings/
  window.keys3dSetFx, keys3d_bg_* keys, keys3d:settings event)
- Combo/accuracy/best-streak DOM HUD (drum_highway_3d pattern), gated on
  a live MIDI session
- tests/fx_settings.test.js (3 tests; vm harness)

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

plugins/keys_highway_3d/plugin.json

@@ -6,6 +6,10 @@
   "type": "visualization",
   "bundled": true,
   "script": "screen.js",
+  "settings": {
+    "html": "settings.html",
+    "category": "graphics"
+  },
   "standards": [
     "capability-pipelines.v1",
     "plugin-runtime-idempotent.v1"