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/angrybirds.js

@@ -1,4 +1,4 @@
-'use strict';
+'use strict';
 
 /* ═══════════════════════════════════════════════════════════════════
    AngryBirdsSim — Angry Birds Physics
@@ -853,3 +853,52 @@ class AngryBirdsSim {
     return `rgb(${r},${g},${b})`;
   }
 }
+
+/* ─── lab UI init ─────────────────────────────────── */
+  var angryBirdsSim = null;
+
+  function _openAngryBirds() {
+    document.getElementById('sim-topbar-title').textContent = 'Angry Birds Physics';
+    _simShow('sim-angrybirds');
+    _simShow('ctrl-angrybirds');
+    requestAnimationFrame(() => requestAnimationFrame(() => {
+      const c = document.getElementById('angrybirds-canvas');
+      if (!angryBirdsSim) {
+        angryBirdsSim = new AngryBirdsSim(c);
+        angryBirdsSim.onUpdate = _abUpdateUI;
+        c.addEventListener('mousedown', e => angryBirdsSim.handleMouseDown(e));
+        c.addEventListener('mousemove', e => angryBirdsSim.handleMouseMove(e));
+        c.addEventListener('mouseup',   e => angryBirdsSim.handleMouseUp(e));
+        c.addEventListener('mouseleave', e => angryBirdsSim.handleMouseUp(e));
+        _addTouchSupport(c, angryBirdsSim);
+      }
+      angryBirdsSim.fit();
+      angryBirdsSim.start();
+    }));
+  }
+
+  function abLevel(n, btn) {
+    document.querySelectorAll('.ab-lvl-btn').forEach(b => b.classList.remove('active'));
+    if (btn) btn.classList.add('active');
+    if (angryBirdsSim) angryBirdsSim.loadLevel(n);
+  }
+
+  function angryBirdsRestart() {
+    if (angryBirdsSim) angryBirdsSim.restart();
+  }
+
+  function _abUpdateUI(info) {
+    const v = (id, val) => { const el = document.getElementById(id); if (el) el.textContent = val; };
+    v('abbar-v1', info.level);
+    v('abbar-v2', info.birds);
+    v('abbar-v3', info.pigs);
+    v('abbar-v4', info.score.toLocaleString('ru'));
+    v('abbar-v5', info.planet);
+    /* sync level button highlight */
+    document.querySelectorAll('.ab-lvl-btn').forEach((b, i) => {
+      b.classList.toggle('active', i === (info.level - 1));
+    });
+  }
+
+  /* ── quadratic ── */
+