feat: Trust Comparison landing page + directorate selector (Task 10.7)

- Add get_directorate_summary() query for per-directorate patient/drug counts
- Create trust_comparison.py with landing grid and 6-chart dashboard layout
- Wire directorate card clicks and back button through app-state callbacks
- Add TC landing and dashboard CSS per Phase 10 design spec
- Placeholder charts for 6 dashboard graphs (filled in Task 10.8)
- Chart type toggle clears selected directorate when switching modes

dash_app/assets/nhs.css

@@ -397,12 +397,153 @@ body {
     text-align: center;
 }
 
+/* ── Trust Comparison Landing ── */
+.tc-landing {
+    display: flex;
+    flex-direction: column;
+    gap: 24px;
+}
+.tc-landing__header {
+    padding: 0 0 8px;
+}
+.tc-landing__title {
+    font-size: 22px;
+    font-weight: 700;
+    color: var(--nhs-dark-blue);
+    margin: 0 0 4px;
+}
+.tc-landing__desc {
+    font-size: 14px;
+    color: var(--nhs-mid-grey);
+    font-weight: 400;
+    margin: 0;
+}
+.tc-landing__grid {
+    display: grid;
+    grid-template-columns: repeat(3, 1fr);
+    gap: 12px;
+}
+.tc-landing__grid--wide {
+    grid-template-columns: repeat(4, 1fr);
+}
+
+/* Directorate selector cards */
+.tc-card {
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+    padding: 16px 20px;
+    background: var(--nhs-white);
+    border: 1px solid var(--nhs-pale-grey);
+    border-left: 4px solid transparent;
+    cursor: pointer;
+    text-align: left;
+    font-family: inherit;
+    transition: border-color 0.15s, background 0.15s, box-shadow 0.15s;
+}
+.tc-card:hover {
+    border-left-color: var(--nhs-blue);
+    background: #FAFCFF;
+    box-shadow: 0 1px 4px rgba(0, 48, 135, 0.08);
+}
+.tc-card:focus-visible {
+    box-shadow: 0 0 0 3px var(--nhs-yellow);
+    z-index: 1;
+}
+.tc-card__name {
+    font-size: 14px;
+    font-weight: 700;
+    color: var(--nhs-dark-blue);
+    line-height: 1.3;
+}
+.tc-card__stats {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    font-size: 12px;
+    color: var(--nhs-mid-grey);
+}
+.tc-card__stat {
+    font-weight: 400;
+    font-variant-numeric: tabular-nums;
+}
+.tc-card__dot {
+    color: var(--nhs-pale-grey);
+}
+
+/* ── Trust Comparison Dashboard ── */
+.tc-dashboard {
+    display: flex;
+    flex-direction: column;
+    gap: 16px;
+}
+.tc-dashboard__header {
+    display: flex;
+    align-items: center;
+    gap: 16px;
+}
+.tc-dashboard__back {
+    padding: 6px 12px;
+    font-size: 14px;
+    font-weight: 600;
+    font-family: inherit;
+    color: var(--nhs-blue);
+    background: var(--nhs-white);
+    border: 1px solid var(--nhs-pale-grey);
+    cursor: pointer;
+    transition: background 0.15s;
+    white-space: nowrap;
+}
+.tc-dashboard__back:hover {
+    background: #E8F0FE;
+}
+.tc-dashboard__back:focus-visible {
+    box-shadow: 0 0 0 3px var(--nhs-yellow);
+}
+.tc-dashboard__title {
+    font-size: 20px;
+    font-weight: 700;
+    color: var(--nhs-dark-blue);
+    margin: 0;
+}
+
+/* 2×3 chart grid */
+.tc-dashboard__grid {
+    display: grid;
+    grid-template-columns: 1fr 1fr;
+    gap: 16px;
+}
+
+/* Individual chart cell */
+.tc-chart-cell {
+    background: var(--nhs-white);
+    border: 1px solid var(--nhs-pale-grey);
+    display: flex;
+    flex-direction: column;
+}
+.tc-chart-cell__title {
+    padding: 10px 16px;
+    font-size: 13px;
+    font-weight: 700;
+    color: var(--nhs-dark-blue);
+    text-transform: uppercase;
+    letter-spacing: 0.04em;
+    border-bottom: 1px solid var(--nhs-pale-grey);
+}
+
 /* ── Responsive ── */
+@media (max-width: 1200px) {
+    .tc-landing__grid { grid-template-columns: repeat(2, 1fr); }
+    .tc-landing__grid--wide { grid-template-columns: repeat(3, 1fr); }
+}
 @media (max-width: 1024px) {
     .kpi-row { grid-template-columns: repeat(2, 1fr); }
 }
 @media (max-width: 768px) {
     .sidebar { display: none; }
     .main { margin-left: 0; }
+    .sub-header { left: 0; }
     .kpi-row { grid-template-columns: 1fr; }
+    .tc-landing__grid { grid-template-columns: 1fr; }
+    .tc-dashboard__grid { grid-template-columns: 1fr; }
 }