Dash page and smart-serow's palette, boxed widgets, attitude and G-meter

Ported from smart-serow's HUD: the four-colour palette with dark/bright variants
(same theme JSON format, loaded at runtime; YUKART_THEME picks one), StatBox and
StatBoxMain, WhiskeyMark and AccelGraph. The whole app takes its colours from the
palette. Dash: attitude, G-meter, RPM, GNSS speed, pedal, coolant and telltales,
each from its contracts signal; missing and stale draw in subdued.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

pubspec.yaml

@@ -60,6 +60,8 @@ flutter:
   # Exact copies of contracts files (tool/sync-contracts.sh); crosscheck verifies them.
   assets:
     - assets/contracts/checklists/
+    # Palettes: smart-serow's theme JSON format (lib/theme/palette.dart).
+    - assets/themes/
 
   # An image asset can refer to one or more resolution-specific "variants", see
   # https://flutter.dev/to/resolution-aware-images