fix(admissions): render trend with Chart.js instead of scaled SVG

The hand-rolled SVG sparkline used px font sizes inside a 520-wide viewBox
that stretched to the full card width, so labels ballooned ~4x and collided —
and with 10+ years of real data the per-point labels and year ticks
overlapped badly, while the oversized chart stretched the "this year" view.

Replace it with a Chart.js line chart (AdmissionsTrendChart) in a fixed
200px wrapper, matching PerformanceChart: responsive px fonts, auto-skipping
x ticks, auto-scaled y-axis clamped to 0-100, emphasised latest point.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nextjs-app/components/AdmissionsTrendChart.module.css

@@ -0,0 +1,10 @@
+.wrapper {
+    width: 100%;
+    height: 200px;
+}
+
+@media (max-width: 640px) {
+    .wrapper {
+        height: 180px;
+    }
+}