fix(detail): give Results Over Time chart more height on desktop

The trend chart was capped at 280px tall on desktop, squishing the
lines together and making them hard to read. Raise the base
.chartContainer height to 380px in both the primary and secondary
detail views.

Mobile is unaffected: the base value is already overridden to
height:auto by the existing max-width:768px query, where
PerformanceChart's own .chartWrapper carries the canvas height.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB

nextjs-app/components/SecondarySchoolDetailView.module.css

@@ -490,7 +490,10 @@
 /* ── Charts & Map ────────────────────────────────────── */
 .chartContainer {
     width: 100%;
-    height: 280px;
+    /* Taller on desktop so the trend lines have vertical room to separate
+       and read clearly. Mobile overrides this to height:auto below (the
+       max-width:768px query), so this only affects desktop. */
+    height: 380px;
     position: relative;
 }