feat: deep statistical analytics — clinical, symptoms, incidence, env correlation, weekday

Adds a substantial layer of data-backed statistics (all grounded in verified,
clean source data — no fabricated metrics).

Backend (new routers/statistics.py, prefix /api/stats; +106 pytest still green):
- /inpatient-clinical: LOS dist + by-disease quartiles, cost dist + by-disease +
  cost-vs-LOS, outcome counts, admission-route counts, BMI-by-age, KPIs
  (5822 admissions, median LOS 4d, mean ¥6294, cure 99.1%, emergency 47%)
- /symptoms: 主诉 keyword frequencies (发热/咳嗽/肺炎…) + revisit ratio (36%)
- /incidence-rate: per-10k-population standardized rate by district (cases ÷ pop)
- /env-correlation: pollutant×cases Pearson + 7×7 pairwise matrix + PM2.5 scatter
- /temporal: weekday distribution (+ month/yoy returned but UI omits them — data
  is December-only, so seasonality/YoY would be misleading)

Frontend:
- NEW 住院临床分析 page (/analysis/clinical, nav 临床分析): 9 charts + KPI row —
  LOS histogram + box-by-disease, cost histogram + scatter + by-disease, outcome
  donut (severity-colored), admission-route donut, age-band BMI box
- DiseaseAnalysis: 主诉症状词频 horizontal bar + revisit ratio
- DistrictComparison: 标化发病率（每万人）with 病例数↔发病率 toggle (rate is
  epidemiologically correct; raw counts mislead by population)
- EnvironmentalHealth: pollutant-cases correlation bar + 7×7 correlation heatmap +
  PM2.5×cases scatter with least-squares regression line
- TrendAnalysis: 星期就诊分布 + honest "data is December-only" note
- statsApi client + types

Gates: tsc 0 · build ok · functional e2e 43/43 (incl 2 new clinical) · verified
live against real backend data via dev proxy

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/clinical/BoxPlotRows.tsx

@@ -0,0 +1,87 @@
+import { memo } from 'react';
+import { CLINICAL_COLORS } from './chartColors';
+
+export interface BoxRow {
+  label: string;
+  p25: number;
+  median: number;
+  p75: number;
+  n: number;
+}
+
+interface BoxPlotRowsProps {
+  rows: BoxRow[];
+  /** 数值单位后缀，如 "天" / ""。 */
+  unit?: string;
+  /** 标签列宽（px）。 */
+  labelWidth?: number;
+}
+
+/**
+ * 横向箱线图（p25–中位–p75）。Recharts 无原生 box plot，
+ * 故用纯 div 渲染：每行一条从 p25 到 p75 的横条，中位处一根竖向刻度。
+ * 复用于「各病种住院天数」与「年龄别BMI」。
+ */
+export const BoxPlotRows = memo(function BoxPlotRows({
+  rows,
+  unit = '',
+  labelWidth = 96,
+}: BoxPlotRowsProps) {
+  if (!rows || rows.length === 0) {
+    return <div className="text-center py-8 text-text-muted text-sm">暂无数据</div>;
+  }
+
+  // 统一横轴域：覆盖所有行的 p25..p75，留一点边距。
+  const domainMin = Math.min(...rows.map((r) => r.p25));
+  const domainMax = Math.max(...rows.map((r) => r.p75));
+  const span = domainMax - domainMin || 1;
+  const pct = (v: number) => ((v - domainMin) / span) * 100;
+
+  return (
+    <div className="space-y-2.5">
+      {rows.map((r) => {
+        const left = pct(r.p25);
+        const right = pct(r.p75);
+        const width = Math.max(right - left, 0.5);
+        const medianLeft = pct(r.median);
+        return (
+          <div key={r.label} className="flex items-center gap-2 text-[11px]">
+            <div
+              className="shrink-0 truncate text-text-secondary text-right"
+              style={{ width: labelWidth }}
+              title={r.label}
+            >
+              {r.label}
+            </div>
+            <div className="relative flex-1 h-5 rounded bg-bg-hover">
+              {/* p25–p75 箱体 */}
+              <div
+                className="absolute top-1 bottom-1 rounded-sm"
+                style={{
+                  left: `${left}%`,
+                  width: `${width}%`,
+                  backgroundColor: CLINICAL_COLORS.box,
+                  opacity: 0.35,
+                }}
+              />
+              {/* 中位刻度 */}
+              <div
+                className="absolute top-0.5 bottom-0.5 w-[2px] rounded"
+                style={{
+                  left: `${medianLeft}%`,
+                  backgroundColor: CLINICAL_COLORS.boxMedian,
+                }}
+                title={`中位 ${r.median}${unit}`}
+              />
+            </div>
+            <div className="shrink-0 w-28 text-text-muted tabular-nums">
+              {r.p25}–<span className="font-semibold text-text-secondary">{r.median}</span>–{r.p75}
+              {unit}
+              <span className="ml-1 text-[10px] text-text-muted">n={r.n}</span>
+            </div>
+          </div>
+        );
+      })}
+    </div>
+  );
+});