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/probability.js

@@ -1,4 +1,4 @@
-'use strict';
+'use strict';
 /* ══════════════════════════════════════════════════════════════
    ProbabilitySim — probability & law of large numbers
    coin flip · single die · two-dice sum
@@ -569,3 +569,45 @@ class ProbabilitySim {
 }
 
 if (typeof module !== 'undefined') module.exports = ProbabilitySim;
+
+/* ─── lab UI init ─────────────────────────────────── */
+  function _openProbability() {
+    document.getElementById('sim-topbar-title').textContent = 'Теория вероятностей';
+    _simShow('sim-probability');
+    _registerSimState('probability', () => probSim?.getParams(), st => probSim?.setParams(st));
+    if (_embedMode) _startStateEmit('probability');
+    requestAnimationFrame(() => requestAnimationFrame(() => {
+      if (!probSim) {
+        probSim = new ProbabilitySim(document.getElementById('probability-canvas'));
+        probSim.onUpdate = _probUpdateUI;
+      }
+      probSim.fit();
+      probSim.reset();
+      probSim.play();
+    }));
+  }
+
+  function probMode(mode, btn) {
+    document.querySelectorAll('.prob-mode-btn').forEach(b => b.classList.remove('active'));
+    if (btn) btn.classList.add('active');
+    if (probSim) { probSim.setParams({ mode }); probSim.reset(); probSim.play(); }
+  }
+
+  function probPreset(mode, trials) {
+    document.querySelectorAll('.prob-mode-btn').forEach(b => {
+      b.classList.toggle('active', b.textContent.toLowerCase().includes(mode === 'coin' ? 'монет' : mode === 'dice2' ? '2 куб' : 'кубик'));
+    });
+    if (probSim) { probSim.setParams({ mode, trials }); probSim.reset(); probSim.play(); }
+  }
+
+  function _probUpdateUI(info) {
+    const v = (id, val) => { const el = document.getElementById(id); if (el) el.textContent = val; };
+    v('probbar-v1', info.totalTrials);
+    v('probbar-v2', typeof info.maxDeviation === 'number' ? (info.maxDeviation * 100).toFixed(1) + '%' : '—');
+    v('probbar-v3', typeof info.chiSquare === 'number' ? info.chiSquare.toFixed(2) : '—');
+    const modeNames = { coin: 'Монета', dice: 'Кубик', dice2: '2 кубика' };
+    v('probbar-v4', modeNames[info.mode] || info.mode);
+  }
+
+  /* ── bohr atom ── */
+