Fix chart aspect ratio for mobile devices

Add dynamic aspect ratio that adjusts based on screen width,
using 1.2 on mobile (<=768px) vs 2 on desktop to prevent
flat/compressed charts on smaller screens.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/app.js

@@ -48,6 +48,11 @@ const CHART_COLORS = [
   "#9b59b6", // violet
 ];
 
+// Helper to get chart aspect ratio based on screen size
+function getChartAspectRatio() {
+  return window.innerWidth <= 768 ? 1.2 : 2;
+}
+
 // =============================================================================
 // DOM ELEMENTS
 // =============================================================================
@@ -804,7 +809,7 @@ async function updateComparisonChart() {
     options: {
       responsive: true,
       maintainAspectRatio: true,
-      aspectRatio: 2,
+      aspectRatio: getChartAspectRatio(),
       plugins: {
         legend: {
           position: "bottom",
@@ -1068,7 +1073,7 @@ async function openSchoolModal(urn) {
     options: {
       responsive: true,
       maintainAspectRatio: true,
-      aspectRatio: 2,
+      aspectRatio: getChartAspectRatio(),
       plugins: {
         legend: {
           position: "bottom",