M5: Blazor dashboard (MudBlazor + ApexCharts)

- MudBlazor theme (dark default) + responsive drawer/appbar layout + nav.
- DashboardService read model: KPIs with period-over-period deltas, category breakdown,
  "what cost more/less" difference view, monthly trends.
- Pages: Overview (KPI cards + DeltaChip + donut + difference table), Trends (range-select
  bar chart), Meters (list + source status), Import (load reference dataset + CSV dry-run
  preview), Admin (energy types, tariffs). Charts isolated into components to avoid the
  ApexCharts/MudBlazor Color/Format name clashes.
- ReferenceDataImporter: one-click load of all four sheets as a starter dataset (meters,
  tank, tariff history, category memberships) — bundled sample CSVs copied to app output.
- End-to-end render test: import creates meters + consumption; overview/meters/trends/
  import/admin pages all return 200 with KPI cards rendered.

92 tests green (56 Core + 36 integration).

Deferred to polish: dedicated PV & oil/consumable panels, meter-detail page, full admin
CRUD, prev-year trend overlay.

Claude-Session: https://claude.ai/code/session_01WujdMtMJPbxDpDnMeK22rr

src/App/Program.cs

@@ -3,6 +3,7 @@ using MeterVault.Infrastructure;
 using MeterVault.Infrastructure.Options;
 using MeterVault.Infrastructure.Persistence;
 using Microsoft.EntityFrameworkCore;
+using MudBlazor.Services;
 using Serilog;
 
 Log.Logger = new LoggerConfiguration()
@@ -33,6 +34,7 @@ try
         builder.Services.AddMeterVaultIngestion();
     }
 
+    builder.Services.AddMudServices();
     builder.Services.AddRazorComponents()
         .AddInteractiveServerComponents();