feat(icons): add icon theming infrastructure with Catppuccin color remapping

- Remove hand-crafted kindred-icons/ in favor of auto-generated themed icons
- Add icons/mappings/ with FCAD.csv (Tango palette) and kindred.csv (Catppuccin Mocha)
- Add icons/retheme.py script to remap upstream FreeCAD SVG colors
- Generate icons/themed/ with 1,595 themed SVGs (45,300 color replacements)
- BitmapFactory loads icons/themed/ as highest priority before default icons
- 157-color mapping covers the full Tango palette, interpolating between
  4 luminance anchors per color family

Regenerate: python3 icons/retheme.py

icons/themed/Arch_Reference.svg

@@ -0,0 +1,182 @@
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