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/Components/App.razor

@@ -7,6 +7,7 @@
     <base href="/" />
     <ResourcePreloader />
     <link rel="stylesheet" href="@Assets["app.css"]" />
+    <link rel="stylesheet" href="_content/MudBlazor/MudBlazor.min.css" />
     <link rel="stylesheet" href="@Assets["MeterVault.App.styles.css"]" />
     <ImportMap />
     <HeadOutlet />
@@ -16,6 +17,9 @@
     <Routes />
     <ReconnectModal />
     <script src="@Assets["_framework/blazor.web.js"]"></script>
+    <script src="_content/MudBlazor/MudBlazor.min.js"></script>
+    <script src="_content/Blazor-ApexCharts/js/apex-charts.min.js"></script>
+    <script src="_content/Blazor-ApexCharts/js/blazor-apex-charts.min.js"></script>
 </body>
 
 </html>