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/quadratic.js

@@ -1,4 +1,4 @@
-'use strict';
+'use strict';
 /* ══════════════════════════════════════════════════════════════
    QuadraticSim — interactive quadratic equation explorer
    y = ax² + bx + c   ·   discriminant, roots, vertex
@@ -432,3 +432,43 @@ class QuadraticSim {
     cv.addEventListener('touchend', () => { t0 = null; });
   }
 }
+
+/* ─── lab UI init ─────────────────────────────────── */
+  function _openQuadratic() {
+    document.getElementById('sim-topbar-title').textContent = 'Корни квадратного уравнения';
+    _simShow('sim-quadratic');
+    _registerSimState('quadratic', () => quadSim?.getParams(), st => quadSim?.setParams(st));
+    if (_embedMode) _startStateEmit('quadratic');
+    requestAnimationFrame(() => requestAnimationFrame(() => {
+      if (!quadSim) {
+        quadSim = new QuadraticSim(document.getElementById('quadratic-canvas'));
+        quadSim.onUpdate = _quadUpdateUI;
+      }
+      quadSim.fit();
+      quadSim.draw();
+      quadSim._emit();
+    }));
+  }
+
+  function quadParam(name, val) {
+    const v = parseFloat(val);
+    document.getElementById('quad-' + name + '-val').textContent = v % 1 === 0 ? v : v.toFixed(1);
+    if (quadSim) quadSim.setParams({ [name]: v });
+  }
+
+  function quadPreset(a, b, c) {
+    document.getElementById('sl-quad-a').value = a; document.getElementById('quad-a-val').textContent = a;
+    document.getElementById('sl-quad-b').value = b; document.getElementById('quad-b-val').textContent = b;
+    document.getElementById('sl-quad-c').value = c; document.getElementById('quad-c-val').textContent = c;
+    if (quadSim) quadSim.setParams({ a, b, c });
+  }
+
+  function _quadUpdateUI(info) {
+    const v = (id, val) => { const el = document.getElementById(id); if (el) el.textContent = val; };
+    v('qbar-v1', 'D = ' + info.D);
+    v('qbar-v2', info.roots);
+    v('qbar-v3', info.vertex);
+    v('qbar-v4', info.equation);
+  }
+
+  /* ── normal distribution ── */