feedback5 R5: split the battle effect system into modules

public/js/render/fx.js becomes a re-export barrel. Speeds, camera heights, fonts, the kind table and the shared tunables move verbatim into public/js/render/fx/*.js. FxSystem keeps its constructor, clear, update, counts and destroy; the other methods move verbatim into container classes installed on FxSystem.prototype in source order. simSpeeds and fontsReady each stay one instance. The dynamic import of /sim/constants.js stays next to setSimProjectileSpeeds.

public/js/render/fx/speeds.js

@@ -0,0 +1,38 @@
+// public/js/render/fx/speeds.js — sim projectile speeds (one module-level table) and the flight-time lookup.
+
+import { PROJ } from '../style.js';
+
+/**
+ * The sim's projectile speeds (server/sim/constants.js PROJECTILE_SPEEDS — pure data, served read-only at
+ * /sim/constants.js with the rest of the client-side sim, DESIGN §14): a shot's visual flight ends when the sim lands it,
+ * i.e. with its damage number. Loaded once in a browser (the game already has the module from its battle runner);
+ * until it arrives — and in Node, where '/sim/' is no module path — style.js PROJ speeds (a copy the unit tests keep
+ * equal to the sim's) stand in.
+ */
+let simSpeeds = null;
+
+/**
+ * Use the sim's speeds (tiles per game second): `table` = PROJECTILE_SPEEDS by kind, `boomerangReturn` =
+ * BOOMERANG_RETURN_SPEED (the sim's visual kind of a boomerang flying back); null = style.js PROJ only.
+ */
+export function setSimProjectileSpeeds(table, boomerangReturn = null) {
+  if (!table || typeof table !== 'object') { simSpeeds = null; return; }
+  simSpeeds = Object.assign({}, table);
+  if (Number(boomerangReturn) > 0) simSpeeds.boomerangReturn = Number(boomerangReturn);
+}
+
+if (typeof window !== 'undefined' && typeof window.location?.origin === 'string') {
+  import('/sim/constants.js').then((m) => { if (m?.PROJECTILE_SPEEDS) setSimProjectileSpeeds(m.PROJECTILE_SPEEDS, m.BOOMERANG_RETURN_SPEED); }, () => {});
+}
+
+/**
+ * Tiles per game second of a projectile kind ('boomerangReturn': a boomerang's way back): the sim's value, else
+ * style.js PROJ (`speed`; the boomerang's `back`), else 15 for a boomerang (the sim's outbound speed) / 12.
+ */
+export function projSpeed(kind) {
+  const v = simSpeeds ? Number(simSpeeds[kind]) : NaN;
+  if (v > 0) return v;
+  if (kind === 'boomerangReturn') return PROJ.boomerang?.back > 0 ? PROJ.boomerang.back : projSpeed('boomerang');
+  const f = PROJ[kind]?.speed;
+  return f > 0 ? f : kind === 'boomerang' ? 15 : 12;
+}