feat: unique color picker for class types in schedule editor

- Add clickable color picker in schedule legend (16 distinct colors)
- Two-pass smart assignment: explicit colors first, then unused palette slots
- Hide already-used colors from the picker (both explicit and fallback)
- Colors saved to classes section and flow to public site schedule dots
- Expanded palette: rose, orange, amber, yellow, lime, emerald, teal, cyan,
  sky, blue, indigo, violet, purple, fuchsia, pink, red

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types/content.ts

@@ -4,6 +4,7 @@ export interface ClassItem {
   icon: string;
   detailedDescription?: string;
   images?: string[];
+  color?: string;
 }
 
 export interface TeamMember {