refactor: distribute lab-init.js into 34 engine files

lab-init.js: 4098 -> 543 lines (infrastructure + THEORY only)

Each sim's _open*() + UI helpers moved to its engine file:
graph.js, projectile.js, collision.js, magnetic.js, triangle.js,
geometry.js, trigcircle.js, gas.js (molphys), coulomb.js, circuit.js,
reactions.js (chemistry), newton.js (dynamics), chemsandbox.js,
celldivision.js, photosynthesis.js, angrybirds.js, quadratic.js,
normaldist.js, graphtransform.js, pendulum.js, equilibrium.js,
thinlens.js, mirror.js, isoprocess.js, titration.js, refraction.js,
probability.js, bohratom.js, electrolysis.js, waves.js,
crystal.js, orbitals.js, stereo.js, hydrostatics.js

All 34 engine files syntax-checked OK.

frontend/js/labs/equilibrium.js

@@ -1,4 +1,4 @@
-'use strict';
+'use strict';
 
 /**
  * EquilibriumSim — Chemical equilibrium simulation.
@@ -474,3 +474,48 @@ class EquilibriumSim {
 }
 
 if (typeof module !== 'undefined') module.exports = EquilibriumSim;
+
+/* ─── lab UI init ─────────────────────────────────── */
+  function _openEquilibrium() {
+    document.getElementById('sim-topbar-title').textContent = 'Химическое равновесие';
+    _simShow('sim-equilibrium');
+    _registerSimState('equilibrium', () => eqSim?.getParams(), st => eqSim?.setParams(st));
+    if (_embedMode) _startStateEmit('equilibrium');
+    requestAnimationFrame(() => requestAnimationFrame(() => {
+      if (!eqSim) {
+        eqSim = new EquilibriumSim(document.getElementById('equilibrium-canvas'));
+        eqSim.onUpdate = _eqUpdateUI;
+      }
+      eqSim.fit();
+      eqSim.reset();
+      eqSim.play();
+    }));
+  }
+
+  function eqParam(name, val) {
+    const v = parseFloat(val);
+    const ids = { T: 'eq-T-val', Ea_f: 'eq-Eaf-val', Ea_r: 'eq-Ear-val' };
+    const el = document.getElementById(ids[name]);
+    if (el) el.textContent = v;
+    if (eqSim) eqSim.setParams({ [name]: v });
+  }
+
+  function eqPreset(name) {
+    if (eqSim) { eqSim.preset(name); eqSim.play(); }
+    const defs = { default: [300,50,55], exothermic: [280,35,65], endothermic: [350,65,35], excess_A: [300,50,55] };
+    const d = defs[name] || defs.default;
+    document.getElementById('sl-eq-T').value = d[0]; document.getElementById('eq-T-val').textContent = d[0];
+    document.getElementById('sl-eq-Eaf').value = d[1]; document.getElementById('eq-Eaf-val').textContent = d[1];
+    document.getElementById('sl-eq-Ear').value = d[2]; document.getElementById('eq-Ear-val').textContent = d[2];
+  }
+
+  function _eqUpdateUI(info) {
+    const v = (id, val) => { const el = document.getElementById(id); if (el) el.textContent = val; };
+    v('eqbar-v1', info.keq);
+    v('eqbar-v2', info.Q);
+    v('eqbar-v3', info.direction);
+    v('eqbar-v4', info.nA + '|' + info.nB + '|' + info.nC + '|' + info.nD);
+  }
+
+  /* ── thin lens ── */
+