engine: geometry.defeature takes features out of the design for meshing (#433)

Suppresses the SolidCraft features named (holes filled, fillets and chamfers back to
their sharp edges, bosses removed) and rebuilds the design; a feature that cannot be
suppressed alone is merged into its neighbour for meshing only. Kept in the model,
replayed on open, undoable; geometry.defeature.delete turns them back on.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

assets/icons/geometry.defeature.svg

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="24" height="24" viewBox="0 0 24 24">
+  <title>geometry.defeature</title>
+  <g id="Layer_1" data-name="Layer 1">
+    <path d="M3 8 L12 4 L21 8 L12 12 Z" fill="#2d4e70" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8" fill="none" stroke="#dde2ea" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M9 8 C9 8.828 10.343 9.5 12 9.5 C13.657 9.5 15 8.828 15 8 C15 7.172 13.657 6.5 12 6.5 C10.343 6.5 9 7.172 9 8 Z" fill="#f0b44a" stroke="#f0b44a" stroke-linecap="round" stroke-linejoin="round"/>
+    <path d="M7.5 11 L16.5 5" fill="none" stroke="#4f9ce8" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"/>
+  </g>
+</svg>

assets/icons/src/geometry.defeature.json

@@ -0,0 +1 @@
+{"shapes": [{"d": "M3 8 L12 4 L21 8 L12 12 Z", "fill": "soft", "stroke": "line"}, {"d": "M3 8 L3 16 L12 20 L12 12 M12 20 L21 16 L21 8", "stroke": "line"}, {"d": "M9 8 A3 1.5 0 1 0 15 8 A3 1.5 0 1 0 9 8 Z", "fill": "warm", "stroke": "warm", "width": 1}, {"d": "M7.5 11 L16.5 5", "stroke": "accent", "width": 1.75}]}