refactor(h3d-carve-8): extract Q-helpers (lighting/FX) → src/fx.js

Six functions extracted from Q-section of screen.js into a new
src/fx.js ES module behind a createFx({...}) factory:
  _h3dHexOrDefault, _applyCinematic, _timingHex,
  _sparkBurst, _sparkUpdate, _bloomEnsure

buildBoard (330 lines) deferred to plan §3 row 16 (P-section cut):
its write-back surface spans 9 factory-scope vars owned by P/U/Y —
premature extraction would require ~50 DI params. See plans/highway3d-carve.md.

DI surface (26 beyond-subst rewires):
  BG_DEFAULTS, K          — plain IIFE-scope constants
  getT                    — live-accessor (Three.js, lazy)
  getAmbLight/getDirLight/getCinematic/getTimingFx — live-accessors
  getSparkPts/.../getSparkN — live-accessors (per-call, not init-cached)
  setSparkPts/setSparkPos/setSparkVel/setSparkCol/setSparkLife — setters
  getComposer/setComposer — getter+setter (_bloomEnsure lazy reassigns)
  getBloomLoad/setBloomLoad/getBloomPass/setBloomPass — getter+setter pairs
  getBloomW/setBloomW/getBloomH/setBloomH — getter+setter pairs
  getRen/getScene/getCam/getHighwayCanvas — live-accessors (null pre-init)
  canvasSize              — factory function ref (stable)

Class-killers (all mutations verified RED before commit):
  - _timingHex EARLY branch removed → RED
  - _sparkBurst stale init-time sparkPos cache → RED (live-accessor required)
  - setBloomLoad silenced → RED (synchronous write-back path)
  - setComposer getComposer init-cached → RED (live getComposer() required)
  GAP declared: setComposer(comp) inside .then() (async, no import() mock)

Tests: 1266/1268 (2 pre-existing failures unrelated to this cut)
plugin.json: 3.43.0 → 3.44.0

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014uZ169yfoFYArXz962g7KW

plugins/highway_3d/plugin.json

@@ -1,7 +1,7 @@
 {
   "id": "highway_3d",
   "name": "3D Highway",
-  "version": "3.43.0",
+  "version": "3.44.0",
   "type": "visualization",
   "scriptType": "module",
   "bundled": true,