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/thinlens.js

@@ -1,4 +1,4 @@
-'use strict';
+'use strict';
 /* ══════════════════════════════════════════════════════════════
    ThinLensSim — thin lens ray tracing simulation
    1/f = 1/d + 1/d'   M = -d'/d
@@ -444,3 +444,46 @@ class ThinLensSim {
     });
   }
 }
+
+/* ─── lab UI init ─────────────────────────────────── */
+  function _openThinLens() {
+    document.getElementById('sim-topbar-title').textContent = 'Тонкая линза';
+    _simShow('sim-thinlens');
+    _registerSimState('thinlens', () => lensSim?.getParams(), st => lensSim?.setParams(st));
+    if (_embedMode) _startStateEmit('thinlens');
+    requestAnimationFrame(() => requestAnimationFrame(() => {
+      if (!lensSim) {
+        lensSim = new ThinLensSim(document.getElementById('thinlens-canvas'));
+        lensSim.onUpdate = _lensUpdateUI;
+      }
+      lensSim.fit();
+      lensSim.draw();
+      lensSim._emit();
+    }));
+  }
+
+  function lensParam(name, val) {
+    const v = parseFloat(val);
+    const ids = { f: 'lens-f-val', d: 'lens-d-val', h: 'lens-h-val' };
+    const el = document.getElementById(ids[name]);
+    if (el) el.textContent = v;
+    if (lensSim) lensSim.setParams({ [name]: v });
+  }
+
+  function lensPreset(f, d, h) {
+    document.getElementById('sl-lens-f').value = f; document.getElementById('lens-f-val').textContent = f;
+    document.getElementById('sl-lens-d').value = d; document.getElementById('lens-d-val').textContent = d;
+    document.getElementById('sl-lens-h').value = h; document.getElementById('lens-h-val').textContent = h;
+    if (lensSim) lensSim.setParams({ f, d, h });
+  }
+
+  function _lensUpdateUI(info) {
+    const v = (id, val) => { const el = document.getElementById(id); if (el) el.textContent = val; };
+    v('lensbar-v1', info.f);
+    v('lensbar-v2', info.dPrime === Infinity ? '∞' : info.dPrime);
+    v('lensbar-v3', info.M === Infinity ? '∞' : info.M);
+    v('lensbar-v4', info.imageType);
+  }
+
+  /* ── mirrors ── */
+