feat: Phase 2 — leadership 大屏 (/overview) + district normalization + drawer a11y

Phase 2 of the UX modernization. Three conflict-free workstreams.

Leadership 驾驶舱 (/overview):
- Wuhan 13-district Leaflet choropleth (public/wuhan_districts.geojson, keyed
  on name, darker=higher per 高风险高亮), legend, hover/click-zoom
- 全部/门诊/住院 Segmented toggle drives choropleth + Top-5 district bar
- literal "数据截至2023-12" as-of badge (D3 honesty); raw spinner → LoadingState
- decompose OverviewDashboard 501→273; 6 components + 2 helpers under components/overview/

District normalization (backend data boundary):
- case_loader.normalize_district + load_cases_by_district_daily collapse the
  26 dirty labels (武昌/武昌区…) → 13 canonical; analysis/grid/insights repointed
  (fixes a grid-merge row-drop bug as a bonus); in-memory, schema unchanged

Shell a11y (code-review carryover):
- drawer is now a proper modal: ESC, body scroll-lock, focus-in + focus-trap
  cycle + focus-restore, role=dialog/aria-modal/aria-label, hamburger aria-expanded
- SideNav expanded state lifted to AppShell so rail+drawer stay in sync
- RouteErrorBoundary around <Outlet/> keeps shell chrome on page/chunk failure

Gates: tsc 0 · vitest 64 · e2e 19/19 (17 user-flows + 2 overview) · build ok
· backend pytest 6 new + 48 regression green

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

backend/routers/insights.py

@@ -11,6 +11,7 @@ from pydantic import BaseModel, Field
 from typing import Dict, List, Literal
 
 from config import DATA_DIR, RISK_HIGH, PROJECT_ROOT
+from data.case_loader import load_cases_by_district_daily
 from models import (
     InsightsResponse,
     InsightTrend,
@@ -491,22 +492,22 @@ async def get_insights_cards():
 
         cases_path = PROJECT_ROOT / "processed" / "cases_by_district_daily.parquet"
         if cases_path.exists():
-            cases_df = _cached_parquet(str(cases_path))
+            # Districts already normalized to the canonical 13 区-suffixed names.
+            cases_df = load_cases_by_district_daily()
+            cases_df["date"] = pd.to_datetime(cases_df["date"])
             latest_case_date = cases_df["date"].max()
-            latest_cases = cases_df[cases_df["date"] == latest_case_date].copy()
-            latest_cases["base_district"] = latest_cases["district"].str.replace("区", "")
-            district_daily = latest_cases.groupby("base_district")["total_cases"].sum().sort_values(ascending=False)
+            latest_cases = cases_df[cases_df["date"] == latest_case_date]
+            district_daily = latest_cases.groupby("district")["total_cases"].sum().sort_values(ascending=False)
             total_daily = int(district_daily.sum())
             top_name = district_daily.index[0]
             top_val = int(district_daily.iloc[0])
             num_districts = len(district_daily)
 
             week_ago = latest_case_date - pd.Timedelta(days=6)
-            week_cases = cases_df[cases_df["date"] >= week_ago].copy()
-            week_cases["base_district"] = week_cases["district"].str.replace("区", "")
+            week_cases = cases_df[cases_df["date"] >= week_ago]
             daily_totals = week_cases.groupby("date")["total_cases"].sum()
             avg_daily = int(daily_totals.mean())
-            week_district = week_cases.groupby("base_district")["total_cases"].sum().sort_values(ascending=False)
+            week_district = week_cases.groupby("district")["total_cases"].sum().sort_values(ascending=False)
             week_top_val = int(week_district.iloc[0])
 
             date_str = latest_case_date.strftime("%m月%d日")
@@ -515,8 +516,8 @@ async def get_insights_cards():
                 title=f"日病例统计 ({date_str})",
                 description=(
                     f"最近统计日({date_str})全市{num_districts}个区共记录{total_daily}例儿童呼吸道疾病病例，"
-                    f"{top_name}区{top_val}例为当日最高。近7日日均{avg_daily}例，"
-                    f"{week_district.index[0]}区累计{week_top_val}例居首。"
+                    f"{top_name}{top_val}例为当日最高。近7日日均{avg_daily}例，"
+                    f"{week_district.index[0]}累计{week_top_val}例居首。"
                 ),
                 type="warning",
                 metric="日病例",