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/crystal.js

@@ -1,4 +1,4 @@
-'use strict';
+'use strict';
 
 /* ═══════════════════════════════════════════════
    CrystalSim — 3D crystal lattice (Three.js)
@@ -313,3 +313,26 @@ class CrystalSim {
     this.renderer.render(this.scene, this.camera);
   }
 }
+
+/* ─── lab UI init ─────────────────────────────────── */
+  var crystalSim = null;
+  function _openCrystal() {
+    document.getElementById('sim-topbar-title').textContent = 'Кристаллическая решётка';
+    _simShow('sim-crystal');
+    requestAnimationFrame(() => requestAnimationFrame(() => {
+      if (!crystalSim) {
+        crystalSim = new CrystalSim(document.getElementById('crystal-container'));
+      } else {
+        crystalSim.fit();
+        crystalSim.play();
+      }
+    }));
+  }
+  function setCrystal(type, btn) {
+    document.querySelectorAll('.crystal-type-btn').forEach(b => { b.classList.remove('active'); b.style.borderColor = ''; b.style.color = ''; });
+    btn.classList.add('active');
+    btn.style.borderColor = '#9B5DE5'; btn.style.color = '#9B5DE5';
+    if (crystalSim) crystalSim.setLattice(type);
+  }
+
+  /* ── molecular orbitals (3D) ── */