feat(ui): make Blueprint the default color scheme

- Add the Blueprint scheme: navy canvas, pale blue sheet, dark navy part
  outlines, orange-red rapids and twelve distinct, readable part fills.
- Use it as the settings default and the fallback for unknown scheme names,
  and list it first in Options. Saved scheme choices are kept.
- Run the palette spacing and readability tests over Blueprint and Classic.
- Document the default in nesting-view-colors.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/nesting-view-colors.md

@@ -1,5 +1,16 @@
 # Nesting-view colors
 
+## Default scheme
+
+**Blueprint** is the default for new installs and the fallback for missing or
+unknown scheme names: deep navy canvas, pale blue sheet, dark navy part
+outlines, orange-red rapids and twelve part fills at least ~30 CIE76 apart that
+stay readable with black part IDs and clear of the etch green, the sheet and the
+canvas. A scheme already saved in **Tools > Options** is kept; choose Blueprint
+there to switch an existing install. Classic remains available.
+
+## Workshop
+
 Choose **Tools > Options > Color scheme > Workshop**, then **Save** for a
 high-contrast per-drawing view: