feat(stereo3d): Фаза 5 — deep-link фигур из учебников + клавиатурная a11y

- openSim('stereo:<figure>') и /lab?stereofig=<figure> открывают нужное тело
  (без изменения общего hash-роутера)
- клавиатура на canvas: стрелки=орбита, +/-=зум, R/Home=сброс
- aria-live на readout; bump stereo.js?v=8
- дробление файла на модули отложено по решению пользователя (в бэклоге)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/js/labs/lab-init.js

@@ -124,6 +124,7 @@
     if (id === 'crystal')      _openCrystal();
     if (id === 'orbitals')     _openOrbitals();
     if (id === 'stereo')       _openStereo();
+    if (id.startsWith('stereo:')) { _openStereo(id.split(':')[1]); }
     if (id === 'chemsandbox')    _openChemSandbox();
     if (id === 'celldivision')   _openCellDivision();
     if (id === 'photosynthesis') _openPhotosynthesis();

frontend/js/labs/stereo.js

@@ -112,6 +112,23 @@ class StereoSim {
       this._invalidate();
     }, { passive: false });
 
+    // Keyboard navigation (a11y) — works when the canvas is focused.
+    on(el, 'keydown', e => {
+      const STEP = 0.12;
+      let handled = true;
+      switch (e.key) {
+        case 'ArrowLeft':  this._rotY -= STEP; this._autoSpin = false; break;
+        case 'ArrowRight': this._rotY += STEP; this._autoSpin = false; break;
+        case 'ArrowUp':    this._rotX = Math.min(1.4, this._rotX + STEP); this._autoSpin = false; break;
+        case 'ArrowDown':  this._rotX = Math.max(-1.4, this._rotX - STEP); this._autoSpin = false; break;
+        case '+': case '=': this._dist = Math.max(4, this._dist - 1); break;
+        case '-': case '_': this._dist = Math.min(40, this._dist + 1); break;
+        case 'r': case 'R': case 'Home': this.resetView(); break;
+        default: handled = false;
+      }
+      if (handled) { e.preventDefault(); this._idleTime = 0; this._invalidate(); }
+    });
+
     // WebGL context loss / restore — keep the page alive if the GPU resets.
     on(el, 'webglcontextlost', e => { e.preventDefault(); this._contextLost = true; this.stop(); }, false);
     on(el, 'webglcontextrestored', () => {
@@ -3706,10 +3723,14 @@ class StereoSim {
     dodecahedron:   ['a'],
   };
 
-  function _openStereo() {
+  function _openStereo(figureType) {
     document.getElementById('sim-topbar-title').textContent = 'Стереометрия 3D';
     _simShow('sim-stereo');
     document.getElementById('stereo-stats').style.display = '';
+    // Deep-link from a textbook: openSim('stereo:pyramid') or /lab?stereofig=pyramid
+    if (!figureType) {
+      try { figureType = new URLSearchParams(location.search).get('stereofig') || null; } catch (_) {}
+    }
     requestAnimationFrame(() => requestAnimationFrame(() => {
       if (!stereoSim) {
         stereoSim = new StereoSim(document.getElementById('stereo-container'));
@@ -3718,6 +3739,10 @@ class StereoSim {
         stereoSim.fit();
         stereoSim.play();
       }
+      if (figureType && STEREO_PARAM_MAP[figureType]) {
+        const btn = document.querySelector(`.stereo-fig-btn[onclick*="'${figureType}'"]`);
+        setStereoFigure(figureType, btn);
+      }
       _stereoShowParams(stereoSim.figureType || 'cube');
       _stereoUpdateUI(stereoSim.info());
       _stereoUpdateFormulas();