feat(keys_highway_3d): anti-plastic materials, studio env, themes, gradient sky, cinematic + glow (K3) (#711)

- Note gems -> MeshPhysicalMaterial: clearcoat 1.0/0.18, roughness 0.32,
  envMapIntensity 0.9 — lacquered glass, not plastic (the explicit ask)
- _makeStudioEnv (PORTED drum_highway_3d): PMREM studio -> scene.environment;
  black keys 0.22 roughness / 1.3 envInt (glossy piano black), whites
  0.42/0.55 ivory, floor 0.55/0.15/0.4 stage sheen
- Vertical-gradient background (light horizon -> theme clear -> dark deck),
  sRGB-tagged for the composer path
- BG_THEMES port (guitar ids/values; keys 'default' = original palette;
  themes drive gradient/fog/floor/rails, never the pitch-class colors);
  keys3dSetTheme + keys3d_bg_theme, live _applyTheme
- Cinematic lighting toggle (0.55/1.3 on; stock 0.75/1.1 off); Glow slider
  across NOTE_EMISSIVE_BASE / consume-flash / key approach-glow
- Env RT + gradient texture disposed in teardown
- Tests: theme table parity + default preservation (28 total)

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

plugins/keys_highway_3d/tests/fx_settings.test.js

@@ -109,3 +109,27 @@ test('FX defaults: hit-FX + vibrancy controls ship enabled', () => {
     assert.equal(FX_DEFAULTS.hitFx, 0.7);
     assert.equal(FX_DEFAULTS.vibrancy, 0.85);
 });
+
+test('themes: table ids match the guitar highway, default is the stock palette', () => {
+    const { BG_THEMES, _bgThemeColors, readThemeSetting } = load().slopsmithViz_keys_highway_3d.__test;
+    assert.deepEqual(Object.keys(BG_THEMES), [
+        'default', 'midnight', 'charcoal', 'deeppurple', 'forest', 'warmslate',
+        'deepfocus', 'deepsea', 'cathode', 'cathodegreen', 'hearth',
+    ]);
+    // 'default' preserves THIS plugin's original look.
+    assert.equal(BG_THEMES.default.clear, 0x1a1a2e);
+    assert.equal(BG_THEMES.default.board, 0x141422);
+    assert.equal(BG_THEMES.default.laneDim, 0x2a2a3e);
+    assert.equal(_bgThemeColors('nonsense'), BG_THEMES.default);
+    assert.equal(readThemeSetting(), 'default'); // no localStorage in the vm
+    for (const [id, t] of Object.entries(BG_THEMES)) {
+        assert.equal(t.clear, t.fog, id + ' clear==fog (horizon dissolve)');
+        assert.ok(t.laneDim != null, id + ' rail color');
+    }
+});
+
+test('FX defaults: theme-PR controls ship enabled at stock-neutral values', () => {
+    const { FX_DEFAULTS } = load().slopsmithViz_keys_highway_3d.__test;
+    assert.equal(FX_DEFAULTS.cinematic, true);
+    assert.equal(FX_DEFAULTS.glow, 0.5);   // 0.5 = 1.0x multiplier (stock)
+});