Refactor site structure and add comprehensive interactive index

- Move Puzzles and Miscellany under Themes
- Add Contest Problems as new theme
- Create About page with comprehensive site information
- Create InteractiveIndex component with advanced filtering and sorting
- Update navigation to include Index, Themes, and About
- Add pagination (10 items per page) with search and tag filtering
- Update routing structure for new theme organization
- Remove standalone Puzzles and Miscellany pages
- Add new theme pages: /themes/puzzles, /themes/miscellany, /themes/contest-problems
- Update homepage to point to new interactive index
- Maintain consistent layout and styling across all new pages

src/pages/Index.tsx

@@ -23,14 +23,14 @@ const Index = () => {
           
           <div className="flex justify-center gap-4 mb-16">
             <Button asChild size="lg" className="bg-accent hover:bg-accent/90">
-              <Link to="/themes" className="inline-flex items-center">
-                Explore Themes
+              <Link to="/index" className="inline-flex items-center">
+                Browse All Interactives
                 <ArrowRight className="ml-2 w-4 h-4" />
               </Link>
             </Button>
             <Button asChild variant="outline" size="lg">
-              <Link to="/puzzles">
-                Try Puzzles
+              <Link to="/themes">
+                Explore Themes
               </Link>
             </Button>
           </div>