fix(labs): SVG markup rendered as text in 6 simulations

Hardcoded inline <svg class="ic"> markers used as arrow replacements

(left over from emoji removal) were displayed as raw HTML text where

the consumer used textContent or canvas fillText:

- chemsandbox: csbar-v5 (Продукты cell) used textContent → SVG visible.

  Switched to innerHTML for consistency with eq/ionNet cells.

  Quiz question (qEl.textContent) and answer also receiving SVG —

  cleaned via _csClean at source.

- reactions: modeTxt drawn via canvas fillText — replaced SVG with →.

- ionexchange: REACTIONS data + canvas labels — bulk SVG → Unicode arrows.

- newton: action button labels used textContent → switched to innerHTML;

  canvas arrow labels: SVG → Unicode →/↓.

- collision: 'KE сохранена' canvas label — SVG checkmark → ✓.

- projectile: canvas badges + textContent wind label — SVG → Unicode ←/→/↩.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/js/labs/reactions.js

@@ -564,7 +564,7 @@ class ReactionSim {
     ctx.fillText('C', ex + ew, toY(pE) - 4);
 
     // Mode label at bottom
-    const modeTxt = { forward: '<svg class="ic" viewBox="0 0 24 24"><line x1="5" y1="12" x2="19" y2="12"/><polyline points="12 5 19 12 12 19"/></svg>  A + B <svg class="ic" viewBox="0 0 24 24"><line x1="5" y1="12" x2="19" y2="12"/><polyline points="12 5 19 12 12 19"/></svg> C', reversible: '⇌  A + B ⇌ C', chain: 'цепная реакция' }[this.mode] || '';
+    const modeTxt = { forward: '→  A + B → C', reversible: '⇌  A + B ⇌ C', chain: 'цепная реакция' }[this.mode] || '';
     ctx.fillStyle = 'rgba(255,255,255,0.22)';
     ctx.font = '8px sans-serif';
     ctx.textAlign = 'center';