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/bohratom.js

@@ -1,4 +1,4 @@
-'use strict';
+'use strict';
 /* ══════════════════════════════════════════════════════════════
    BohrAtomSim — Bohr atomic model simulation (hydrogen)
    E_n = −13.6 / n²  eV      λ = 1240 / ΔE  nm
@@ -638,3 +638,43 @@ class BohrAtomSim {
     });
   }
 }
+
+/* ─── lab UI init ─────────────────────────────────── */
+  function _openBohrAtom() {
+    document.getElementById('sim-topbar-title').textContent = 'Атом Бора';
+    _simShow('sim-bohratom');
+    _registerSimState('bohratom', () => bohrSim?.getParams(), st => bohrSim?.setParams(st));
+    if (_embedMode) _startStateEmit('bohratom');
+    requestAnimationFrame(() => requestAnimationFrame(() => {
+      if (!bohrSim) {
+        bohrSim = new BohrAtomSim(document.getElementById('bohratom-canvas'));
+        bohrSim.onUpdate = _bohrUpdateUI;
+      }
+      bohrSim.fit();
+      bohrSim.play();
+    }));
+  }
+
+  function bohrLevel(n) {
+    if (bohrSim) {
+      const from = bohrSim.info().level;
+      if (from !== n) bohrSim.transition(from, n);
+    }
+  }
+
+  function bohrTransition(from, to) {
+    if (bohrSim) bohrSim.transition(from, to);
+  }
+
+  function _bohrUpdateUI(info) {
+    const v = (id, val) => { const el = document.getElementById(id); if (el) el.textContent = val; };
+    v('bohrbar-v1', info.level);
+    v('bohrbar-v2', info.energy.toFixed(2));
+    if (info.lastTransition) {
+      v('bohrbar-v3', info.lastTransition.wavelength.toFixed(0));
+      v('bohrbar-v4', info.lastTransition.series || '—');
+    }
+  }
+
+  /* ── electrolysis ── */
+