feat: add reports center, admin drill-down, disease filter + bug fixes + perf optimization

Frontend features:
- 报表中心 (ReportsCenter): list/detail views, diagnosis breakdown chart, CSV export
- 多级行政下钻 (AdminBreadcrumb): 湖北省→武汉市→区→街道 hierarchical drill-down
- 按病种筛选 (DiseaseFilter): multi-select diagnosis filter on monitoring + reports pages

Backend:
- Add /forecast/{days} endpoint, diagnosis filter params on cases endpoints
- Add /streets aggregation endpoint, enrich reports with real case data
- Extract shared case_loader module

Bug fixes (14):
- Fix missing /risk/forecast route (404), historyApi pointing to non-existent router
- Fix min_risk filter silently ignored in insights/hotspots
- Fix type mismatches: CaseTrendResponse, CaseStatsResponse shapes
- Fix silent .catch(() => {}) swallowing errors, fetchAlerts not clearing stale state
- Fix lru_cache caching exceptions, generateReport used cachedGet for write op
- Fix missing useEffect deps in Insights, DistrictComparison, ReportsCenter

Performance (9):
- Zustand selectors across 9 components (eliminate re-render cascades)
- Fix districtCases.sort() mutating store state, inline IIFE → memo'd component
- CaseLocationMap: React.memo, race protection, correct deps
- AlertCard: stable callbacks, TimelinePlayer: useMemo, TopNav: clock isolation
- SideNav: modules array to module scope, DiseaseFilter: memoized filter

frontend/src/components/TimelinePlayer.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useRef, useCallback } from 'react';
+import { useState, useEffect, useRef, useCallback, useMemo } from 'react';
 import { Play, Pause, SkipBack, SkipForward } from 'lucide-react';
 
 interface TimelinePlayerProps {
@@ -40,9 +40,9 @@ export function TimelinePlayer({
     return dates;
   }, []);
 
-  const dateRange = generateDateRange(startDate, endDate);
-  const currentIndex = dateRange.indexOf(currentDate);
-  const progress = ((currentIndex + 1) / dateRange.length) * 100;
+  const dateRange = useMemo(() => generateDateRange(startDate, endDate), [startDate, endDate, generateDateRange]);
+  const currentIndex = useMemo(() => dateRange.indexOf(currentDate), [dateRange, currentDate]);
+  const progress = useMemo(() => ((currentIndex + 1) / dateRange.length) * 100, [currentIndex, dateRange.length]);
 
   const play = useCallback(() => {
     setPlaying(true);