feat: simmetria 'invariante' per oggetti circolari (1 variante angolare)

Test tooth_rim foro grande: 12x piu veloce (0.14s vs 1.77s) perche
angle_max=0 genera 1 sola variante angolare invece di 72.

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

pm2d/web/static/app.js

@@ -202,7 +202,7 @@ async function doMatch() {
   let body;
   if (hasAdv) {
     // Merge simple → tecnici base, poi overrides
-    const SYM_MAP = {nessuna:360, bilaterale:180, rot_3:120,
+    const SYM_MAP = {invariante:0, nessuna:360, bilaterale:180, rot_3:120,
                      rot_4:90, rot_6:60, rot_8:45};
     const SCALE_MAP = {fissa:[1,1,0.1], mini:[0.9,1.1,0.05],
                        medio:[0.75,1.25,0.05], max:[0.5,1.5,0.05]};