feat: remove cost/费用 statistics from clinical analytics

Per request — drop all monetary statistics (住院费用 is sensitive).
- Backend statistics.py: remove mean_cost KPI + cost_histogram / cost_by_disease
  / cost_vs_los from /inpatient-clinical (models, computation, response)
- Frontend: drop 人均费用 KPI card (now 4 KPIs), 住院费用分布, 各病种平均费用,
  费用×住院天数散点; delete CostByDiseaseChart + CostVsLosScatter components;
  trim statsApi type + e2e fixture + chartColors

Clinical page now: KPI(总人次/中位住院日/治愈好转率/急诊占比) + LOS dist + LOS-by-disease
box + outcome donut + admission-route donut + age-band BMI box.

Gates: backend 106 pytest · tsc 0 · build ok · clinical+user-flows e2e 19/19 ·
live endpoint confirmed cost-free

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

frontend/src/components/clinical/ClinicalKpiRow.tsx

@@ -1,5 +1,5 @@
 import { memo } from 'react';
-import { Users, CalendarDays, Wallet, HeartPulse, Siren } from 'lucide-react';
+import { Users, CalendarDays, HeartPulse, Siren } from 'lucide-react';
 import { StatCard } from '@/components/StatCard';
 import { TESTIDS } from '@/utils/testids';
 import type { InpatientClinicalResponse } from '@/services/api';
@@ -8,12 +8,12 @@ interface ClinicalKpiRowProps {
   kpis: InpatientClinicalResponse['kpis'];
 }
 
-/** 住院临床 5 项核心指标。375px 下 2 列，sm 起 5 列。 */
+/** 住院临床 4 项核心指标。375px 下 2 列，sm 起 4 列。 */
 export const ClinicalKpiRow = memo(function ClinicalKpiRow({ kpis }: ClinicalKpiRowProps) {
   return (
     <div
       data-testid={TESTIDS.clinicalKpis}
-      className="grid grid-cols-2 sm:grid-cols-5 gap-3"
+      className="grid grid-cols-2 sm:grid-cols-4 gap-3"
     >
       <StatCard
         icon={<Users className="w-4 h-4 text-primary" />}
@@ -25,11 +25,6 @@ export const ClinicalKpiRow = memo(function ClinicalKpiRow({ kpis }: ClinicalKpi
         label="中位住院日"
         value={`${kpis.median_los_days} 天`}
       />
-      <StatCard
-        icon={<Wallet className="w-4 h-4 text-primary" />}
-        label="人均费用"
-        value={`¥${Math.round(kpis.mean_cost).toLocaleString()}`}
-      />
       <StatCard
         icon={<HeartPulse className="w-4 h-4 text-success" />}
         label="治愈好转率"