Polish/audit: fix bugs found by 3 subsystem audits

Correctness/data:
- Fix demo cost double-count: reference importer no longer imports the Kosten Strom/Wasser
  columns for categories that are metered (only Heizung), so Wasser rollup is 70€ not 140€.
- Spurious-decrease guard: only a reset/swap in the window (prevReading, thisReading] explains
  a decrease — an old historical reset no longer permanently disables the guard.
- Gate swap auto-detection on MappingProfile.DetectCumulativeSwaps (flag was ignored).
- Prorate basePrice by bucket length (day/month/year); guard virtual expressions against NaN/Inf.

Concurrency/infra:
- Blazor: register a DbContextFactory; CostService/DashboardService and the read pages now use
  short-lived per-operation contexts (no shared circuit DbContext); guard Trends re-entrancy.
- /events: wrap event insert + consumption recompute in one transaction (atomic); 404 (not 500)
  on unknown meter.
- MQTT worker: subscribe to newly-added topics on each tick; move client cleanup into finally.
- Migrations: CREATE MATERIALIZED VIEW IF NOT EXISTS + if_not_exists on CAgg/compression/
  hypertable calls (re-run-safe after a mid-migration crash).
- HA worker: prune stale poll-schedule entries; export: null dangling ImportBatchIds on restore.

API/security:
- API fail-closed by default: with no keys and AllowAnonymousApi off, /api/v1 returns 401
  (protects /export and /import). New MeterVault:AllowAnonymousApi opt-in.
- Cap /readings batch at 5000; report ignored (unknown-meter) count; enums as strings in JSON.

+4 regression tests (guard window, API closed, /events 404, no demo double-count). 98 tests
green; Docker deploy re-verified healthy with the API fail-closed.

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

src/App/Components/Pages/Admin/EnergyTypes.razor

@@ -1,6 +1,6 @@
 @page "/admin/energy-types"
 @rendermode InteractiveServer
-@inject MeterVault.Infrastructure.Persistence.MeterVaultDbContext Db
+@inject Microsoft.EntityFrameworkCore.IDbContextFactory<MeterVault.Infrastructure.Persistence.MeterVaultDbContext> DbFactory
 @using Microsoft.EntityFrameworkCore
 
 <PageTitle>MeterVault — Energy types</PageTitle>
@@ -32,6 +32,9 @@ else
 @code {
     private List<EnergyType>? _types;
 
-    protected override async Task OnInitializedAsync() =>
-        _types = await Db.EnergyTypes.AsNoTracking().OrderBy(t => t.Id).ToListAsync();
+    protected override async Task OnInitializedAsync()
+    {
+        await using var db = await DbFactory.CreateDbContextAsync();
+        _types = await db.EnergyTypes.AsNoTracking().OrderBy(t => t.Id).ToListAsync();
+    }
 }

src/App/Components/Pages/Admin/Tariffs.razor

@@ -1,6 +1,6 @@
 @page "/admin/tariffs"
 @rendermode InteractiveServer
-@inject MeterVault.Infrastructure.Persistence.MeterVaultDbContext Db
+@inject Microsoft.EntityFrameworkCore.IDbContextFactory<MeterVault.Infrastructure.Persistence.MeterVaultDbContext> DbFactory
 @using Microsoft.EntityFrameworkCore
 
 <PageTitle>MeterVault — Tariffs</PageTitle>
@@ -40,8 +40,11 @@ else
 @code {
     private List<Tariff>? _tariffs;
 
-    protected override async Task OnInitializedAsync() =>
-        _tariffs = await Db.Tariffs.AsNoTracking()
+    protected override async Task OnInitializedAsync()
+    {
+        await using var db = await DbFactory.CreateDbContextAsync();
+        _tariffs = await db.Tariffs.AsNoTracking()
             .OrderBy(t => t.Component).ThenBy(t => t.ValidFrom)
             .ToListAsync();
+    }
 }