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/TopNav.tsx

@@ -0,0 +1,57 @@
+import { useState, useEffect } from 'react';
+
+interface TopNavProps {
+  onLogout?: () => void;
+}
+
+export function TopNav({ onLogout }: TopNavProps) {
+  const [currentTime, setCurrentTime] = useState('');
+
+  useEffect(() => {
+    const update = () => setCurrentTime(new Date().toLocaleString('zh-CN'));
+    update();
+    const timer = setInterval(update, 1000);
+    return () => clearInterval(timer);
+  }, []);
+
+  return (
+    <nav className="h-[52px] bg-bg-card border-b border-border flex items-center px-5 fixed top-0 left-0 right-0 z-50">
+      <div className="flex items-center gap-3">
+        <div className="w-7 h-7 bg-primary rounded-md flex items-center justify-center">
+          <svg className="w-4 h-4 fill-white" viewBox="0 0 24 24">
+            <path d="M19 3H5c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h14c1.1 0 2-.9 2-2V5c0-1.1-.9-2-2-2zm-7 3c1.93 0 3.5 1.57 3.5 3.5S13.93 13 12 13s-3.5-1.57-3.5-3.5S10.07 6 12 6zm7 13H5v-.23c0-.62.28-1.2.76-1.58C7.47 15.82 9.64 15 12 15s4.53.82 6.24 2.19c.48.38.76.97.76 1.58V19z"/>
+          </svg>
+        </div>
+        <span className="font-display font-semibold text-[15px] text-text-primary">
+          WuhanChildRisk
+        </span>
+      </div>
+
+      <div className="w-px h-5 bg-border ml-4 mr-4" />
+
+      <span className="text-[13px] text-text-secondary">
+        儿童呼吸道疾病风险监测预警平台
+      </span>
+
+      <div className="ml-auto flex items-center gap-5">
+        <span className="text-[12px] text-text-muted">
+          {currentTime}
+        </span>
+        <div className="flex items-center gap-2 text-[13px] text-text-secondary">
+          <svg className="w-4 h-4" fill="currentColor" viewBox="0 0 24 24">
+            <path d="M12 12c2.21 0 4-1.79 4-4s-1.79-4-4-4-4 1.79-4 4 1.79 4 4 4zm0 2c-2.67 0-8 1.34-8 4v2h16v-2c0-2.66-5.33-4-8-4z"/>
+          </svg>
+          admin
+        </div>
+        {onLogout && (
+          <button
+            onClick={onLogout}
+            className="text-[12px] text-text-muted hover:text-danger transition-colors"
+          >
+            退出
+          </button>
+        )}
+      </div>
+    </nav>
+  );
+}