Add Presents Puzzle interactive to Discrete Math > Uncertainty

Created a new interactive puzzle that explores probability and search strategies:
- Alice opens boxes in sequential order (1, 2, 3, ...)
- Bob opens odds first, then evens (1, 3, 5, ..., 2, 4, 6, ...)
- 26 presents randomly distributed in 100 boxes
- Interactive visualization with two 10×10 grids
- Single simulation with animated opening process
- Batch simulation of 100 rounds to analyze win rates
- Added to Uncertainty theme page (first interactive in this category)

src/App.tsx

@@ -59,6 +59,7 @@ import CrapsGamePage from './pages/CrapsGamePage';
 import NeighborSumAvoidancePage from './pages/NeighborSumAvoidancePage';
 import BurnsidesLemmaPage from './pages/BurnsidesLemmaPage';
 import CubeColoringPage from './pages/CubeColoringPage';
+import PresentsPuzzlePage from './pages/PresentsPuzzlePage';
 
 const queryClient = new QueryClient();
 
@@ -87,6 +88,7 @@ const App = () => (
            <Route path="/themes/discrete-math/graphs/neighbor-sum-avoidance" element={<NeighborSumAvoidancePage />} />
            <Route path="/themes/discrete-math/structures/burnsides-lemma" element={<BurnsidesLemmaPage />} />
            <Route path="/themes/discrete-math/structures/cube-coloring" element={<CubeColoringPage />} />
+           <Route path="/themes/discrete-math/uncertainty/presents-puzzle" element={<PresentsPuzzlePage />} />
           <Route path="/themes/social-choice" element={<SocialChoice />} />
           <Route path="/themes/advanced-algorithms" element={<AdvancedAlgorithms />} />
           <Route path="/themes/data-structures" element={<DataStructures />} />