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/theme-pages/ContestProblems.tsx

@@ -0,0 +1,19 @@
+import ComingSoon from "@/components/ComingSoon";
+import Layout from "@/components/Layout";
+
+const ContestProblems = () => {
+  return (
+    <Layout>
+      <div className="py-12 px-4">
+        <div className="max-w-6xl mx-auto">
+          <ComingSoon 
+            title="Contest Problems"
+            description="Practice with problems from programming competitions, mathematical olympiads, and algorithmic challenges with interactive solutions and explanations."
+          />
+        </div>
+      </div>
+    </Layout>
+  );
+};
+
+export default ContestProblems;