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/analysis.py

@@ -12,6 +12,7 @@ import pandas as pd
 from pydantic import BaseModel, Field
 
 from config import DATA_DIR, RISK_HIGH, PROJECT_ROOT, WUHAN_BOUNDS, LAT_STEP, LON_STEP
+from data.case_loader import load_cases_by_district_daily
 from utils.date_helpers import get_latest_date
 from utils.geojson import parse_geojson_file, load_districts
 from utils.geo import point_in_polygon
@@ -179,18 +180,16 @@ def _district_avg_aqi() -> dict:
 def _district_total_cases() -> dict:
     """Real total recorded cases per district from cases_by_district_daily.
 
-    District labels in the case file are inconsistent ("武昌" vs "武昌区"),
-    so names are normalized by stripping the "区" suffix and summed, then
-    keyed by the canonical mapping name (with "区"). Returns {district: cases}.
+    District labels are normalized to the canonical 13 区-suffixed names at the
+    data-access boundary (data.case_loader), so this is a plain per-district
+    sum. Returns {district: cases}.
     """
-    path = PROJECT_ROOT / "processed" / "cases_by_district_daily.parquet"
-    if not path.exists():
+    try:
+        df = load_cases_by_district_daily()
+    except FileNotFoundError:
         return {}
-    df = pd.read_parquet(path, columns=["district", "total_cases"])
-    df = df.copy()
-    df["base"] = df["district"].str.replace("区", "", regex=False)
-    by_base = df.groupby("base")["total_cases"].sum()
-    return {f"{base}区": int(v) for base, v in by_base.items()}
+    by_district = df.groupby("district")["total_cases"].sum()
+    return {str(d): int(v) for d, v in by_district.items()}
 
 
 @lru_cache(maxsize=8)