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

docs/src/development/repo-structure.md

@@ -20,7 +20,10 @@ create/
 ├── mods/                       # Kindred addon workbenches (submodules)
 │   ├── ztools/                 # ztools workbench
 │   └── silo/                   # Silo parts database
-├── kindred-icons/              # SVG icon library (~200 icons)
+├── icons/                      # Icon theming (kindred overrides, palettes, retheme script)
+│   ├── kindred/                # Hand-crafted Catppuccin Mocha SVG overrides (~1444 icons)
+│   ├── mappings/               # Color palette CSVs (FCAD.csv, kindred.csv)
+│   └── retheme.py              # Script to remap upstream icon colors
 ├── resources/                  # Branding, desktop integration
 │   ├── branding/               # Logo, splash, icon generation scripts
 │   └── icons/                  # Platform icons (.ico, .icns, hicolor)