Change theme color from yellow to amber

Yellow was too bright in Material 9.x, amber provides a more
professional appearance while keeping the warm color scheme.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: nbhansen

mkdocs.yml

@@ -17,8 +17,8 @@ theme:
       text: "Open Sans"
       code: "Roboto Mono"
    palette:
-      primary: "yellow"
-      accent: "deep orange"
+      primary: "amber"
+      accent: "orange"
    logo: "extra/giraf.png"
    features:
       - navigation.tabs