feat(admissions): surface multi-year admissions trend on school detail

The school detail page only showed the latest admissions year. We store
every year, which is more decision-relevant for parents (the trend and its
consistency matter more than a single noisy year).

Backend now returns the full admissions_history (oldest first) alongside the
existing latest-year object. The primary SchoolDetailView gains a header
toggle ("This year | N-year trend") that swaps the Q&A for an SVG sparkline
of the first-choice offer rate. The toggle only appears when >=2 years carry
an offer rate; otherwise it falls back to the single-year card. Both views
share one CSS-grid cell so switching causes no layout shift.

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

nextjs-app/components/SchoolDetailView.module.css

@@ -1295,6 +1295,148 @@
     }
 }
 
+/* ── Admissions: header + view toggle ── */
+.admissionsHeader {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    gap: 1rem;
+    flex-wrap: wrap;
+    margin-bottom: 1.25rem;
+}
+
+.admissionsHeader .sectionTitle {
+    margin-bottom: 0;
+}
+
+.admissionsSeg {
+    display: inline-flex;
+    background: var(--bg-secondary, #f3ede4);
+    border-radius: 999px;
+    padding: 3px;
+    gap: 2px;
+    flex: none;
+}
+
+.admissionsSeg button {
+    appearance: none;
+    border: none;
+    background: none;
+    cursor: pointer;
+    font: inherit;
+    font-size: 0.8125rem;
+    font-weight: 600;
+    color: var(--text-muted, #6d685f);
+    padding: 0.4rem 0.9rem;
+    border-radius: 999px;
+    white-space: nowrap;
+    transition: background 0.15s ease, color 0.15s ease;
+}
+
+.admissionsSeg button[aria-pressed="true"] {
+    background: var(--bg-card, #fff);
+    color: var(--text-primary, #1a1612);
+    box-shadow: var(--shadow-soft, 0 2px 8px rgba(26, 22, 18, 0.06));
+}
+
+.admissionsSeg button:hover[aria-pressed="false"] {
+    color: var(--text-secondary, #5c564d);
+}
+
+/* Stack both views in one grid cell so the card sizes to the taller view —
+   toggling modes never shifts layout. */
+.admissionsViewport {
+    display: grid;
+}
+
+.admissionsViewYear,
+.admissionsViewTrend {
+    grid-area: 1 / 1;
+}
+
+.admissionsViewYear[hidden],
+.admissionsViewTrend[hidden] {
+    display: block;
+    visibility: hidden;
+    pointer-events: none;
+}
+
+/* The this-year rows spread to fill the height reserved by the taller view. */
+.admissionsViewYear {
+    display: flex;
+    flex-direction: column;
+}
+
+.admissionsViewYear .admissionsQa {
+    flex: 1;
+    justify-content: space-between;
+}
+
+.admissionsChartCap {
+    font-size: 0.8125rem;
+    font-weight: 600;
+    letter-spacing: 0.04em;
+    text-transform: uppercase;
+    color: var(--text-muted, #6d685f);
+    margin-bottom: 0.5rem;
+}
+
+.admissionsChart {
+    width: 100%;
+    height: auto;
+    display: block;
+}
+
+.admissionsGrid {
+    stroke: var(--border-color, #e5dfd5);
+    stroke-width: 1;
+}
+
+.admissionsAxis {
+    font-size: 12.5px;
+    fill: var(--text-muted, #6d685f);
+    font-family: var(--font-dm-sans), "DM Sans", sans-serif;
+}
+
+.admissionsLine {
+    stroke: var(--accent-coral, #e07256);
+    stroke-width: 3;
+}
+
+.admissionsDot {
+    fill: var(--accent-coral, #e07256);
+}
+
+.admissionsDotLast {
+    fill: var(--accent-coral, #e07256);
+    stroke: var(--bg-card, #fff);
+    stroke-width: 2;
+}
+
+.admissionsPtLabel {
+    font-size: 13px;
+    font-weight: 700;
+    fill: var(--text-primary, #1a1612);
+    font-family: var(--font-dm-sans), "DM Sans", sans-serif;
+}
+
+.admissionsPtLabel[data-last="true"] {
+    fill: var(--accent-coral-dark, #c45a3f);
+}
+
+.admissionsTrendSummary {
+    font-size: 1rem;
+    color: var(--text-secondary, #5c564d);
+    margin: 1.25rem 0 0;
+    padding-top: 1.1rem;
+    border-top: 1px solid var(--border-color, #e5dfd5);
+    line-height: 1.5;
+}
+
+.admissionsTrendSummary strong {
+    color: var(--text-primary, #1a1612);
+}
+
 /* ── History accordion ── */
 .historyDisclosure {
     margin-top: 1rem;