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/e2e/clinical.spec.ts

@@ -10,7 +10,6 @@ const CLINICAL_FIXTURE = {
   kpis: {
     total_admissions: 5822,
     median_los_days: 4,
-    mean_cost: 6294,
     cure_rate: 0.991,
     emergency_admit_ratio: 0.47,
   },
@@ -23,19 +22,6 @@ const CLINICAL_FIXTURE = {
     { diagnosis: '肺炎', p25: 3, median: 5, p75: 7, n: 800 },
     { diagnosis: '支气管炎', p25: 2, median: 4, p75: 6, n: 600 },
   ],
-  cost_histogram: [
-    { bin_label: '0-3k', count: 1800 },
-    { bin_label: '3k-6k', count: 2200 },
-  ],
-  cost_by_disease: [
-    { diagnosis: '肺炎', mean_cost: 7200, n: 800 },
-    { diagnosis: '支气管炎', mean_cost: 5100, n: 600 },
-  ],
-  cost_vs_los: [
-    { los: 3, cost: 5000 },
-    { los: 5, cost: 7200 },
-    { los: 7, cost: 9100 },
-  ],
   outcome_counts: [
     { outcome: '治愈', count: 3474 },
     { outcome: '好转', count: 2298 },