feat: Initial CBPOA commit — 武汉儿童呼吸疾病风险评估系统

Context: Build a spatial risk assessment system correlating air quality
data with children's respiratory disease incidence across Wuhan.

Approach: FastAPI backend serving PostGIS spatial queries, React
frontend with Deck.gl maps, and a PyTorch SpatialTemporalGCN pipeline
for multi-day (1d/3d/7d) risk prediction.

Changes:
- backend/ — FastAPI API with auth (JWT), alerts, risk analysis,
  geocoded case data, grid statistics, and report endpoints
- frontend/ — React dashboard with interactive risk maps, alert
  monitoring, district comparison charts, and timeline player
- models/ — SpatialTemporalGCN model with trained weights and ONNX
  export for inference
- scripts/ — ETL pipeline for weather + medical data, grid generation,
  feature engineering, training, and daily inference
- deploy/ — Docker Compose configs for backend, frontend, and MLflow
- docs/ — API docs, deployment guide, user guide, and code review

Impact: Enables spatial risk visualization, alert monitoring, and
ML-driven health risk forecasting for environmental health teams.

frontend/src/components/StatCard.tsx

@@ -0,0 +1,44 @@
+interface StatCardProps {
+  label: string;
+  value: string | number;
+  change?: string;
+  changeType?: 'up' | 'down' | 'neutral';
+  progress?: number;
+  progressColor?: string;
+}
+
+export function StatCard({
+  label,
+  value,
+  change,
+  changeType = 'neutral',
+  progress,
+  progressColor = 'bg-warning',
+}: StatCardProps) {
+  return (
+    <div className="card p-4">
+      <div className="text-[11px] font-medium text-text-muted uppercase tracking-wide mb-1.5">
+        {label}
+      </div>
+      <div className="font-display text-[26px] font-bold text-text-primary mb-1">
+        {value}
+      </div>
+      {change && (
+        <div className={`text-[11px] ${
+          changeType === 'up' ? 'text-danger' :
+          changeType === 'down' ? 'text-success' : 'text-text-muted'
+        }`}>
+          {change}
+        </div>
+      )}
+      {progress !== undefined && (
+        <div className="h-[3px] bg-bg-page rounded mt-2.5 overflow-hidden">
+          <div
+            className={`h-full rounded ${progressColor}`}
+            style={{ width: `${progress}%` }}
+          />
+        </div>
+      )}
+    </div>
+  );
+}