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/Pages/Meters.razor

@@ -0,0 +1,64 @@
+@page "/meters"
+@rendermode InteractiveServer
+@inject MeterVault.Infrastructure.Persistence.MeterVaultDbContext Db
+@using Microsoft.EntityFrameworkCore
+
+<PageTitle>MeterVault — Meters</PageTitle>
+
+<MudText Typo="Typo.h4" Class="mb-4">Meters</MudText>
+
+@if (_meters is null)
+{
+    <MudProgressLinear Indeterminate="true" Color="Color.Primary" />
+}
+else
+{
+    <MudTable Items="_meters" Dense="true" Hover="true" Elevation="2">
+        <HeaderContent>
+            <MudTh>Name</MudTh>
+            <MudTh>Type</MudTh>
+            <MudTh>Mode</MudTh>
+            <MudTh>Unit</MudTh>
+            <MudTh>Sources</MudTh>
+            <MudTh>Last seen</MudTh>
+        </HeaderContent>
+        <RowTemplate>
+            <MudTd DataLabel="Name">@context.Name</MudTd>
+            <MudTd DataLabel="Type">@context.EnergyType?.DisplayName</MudTd>
+            <MudTd DataLabel="Mode">@context.Mode</MudTd>
+            <MudTd DataLabel="Unit">@context.Unit</MudTd>
+            <MudTd DataLabel="Sources">@context.Sources.Count</MudTd>
+            <MudTd DataLabel="Last seen">
+                @{
+                    var lastSeen = context.Sources
+                        .Where(s => s.LastSeenAt != null)
+                        .Select(s => s.LastSeenAt)
+                        .DefaultIfEmpty(null)
+                        .Max();
+                }
+                @(lastSeen?.ToString("yyyy-MM-dd HH:mm") ?? "—")
+            </MudTd>
+        </RowTemplate>
+    </MudTable>
+
+    @if (_meters.Count == 0)
+    {
+        <MudAlert Severity="Severity.Info" Class="mt-4">
+            No meters yet. Go to <MudLink Href="/import">Import</MudLink> to load the reference data.
+        </MudAlert>
+    }
+}
+
+@code {
+    private List<Meter>? _meters;
+
+    protected override async Task OnInitializedAsync()
+    {
+        _meters = await Db.Meters
+            .AsNoTracking()
+            .Include(m => m.EnergyType)
+            .Include(m => m.Sources)
+            .OrderBy(m => m.EnergyTypeId).ThenBy(m => m.Name)
+            .ToListAsync();
+    }
+}