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

tests/Integration.Tests/Ingestion/IngestionServiceTests.cs

@@ -49,6 +49,28 @@ public sealed class IngestionServiceTests(TimescaleFixture fx)
         await CleanupAsync(db, meterId);
     }
 
+    [Fact]
+    public async Task Old_reset_does_not_permanently_disable_the_decrease_guard()
+    {
+        await using var db = fx.CreateContext();
+        var (meterId, sourceId) = await SetupAsync(db, MeterMode.CumulativeCounter);
+        var service = new IngestionService(db);
+
+        // A reset early on explains an early decrease...
+        await service.IngestAsync(sourceId, T0, 100);
+        db.MeterEvents.Add(new MeterEvent { MeterId = meterId, Time = T0.AddMinutes(10), EventType = MeterEventType.CounterReset, NewValue = 0 });
+        await db.SaveChangesAsync();
+        Assert.Equal(IngestionOutcome.Written, await service.IngestAsync(sourceId, T0.AddMinutes(20), 30));
+        await service.IngestAsync(sourceId, T0.AddHours(1), 200);
+
+        // ...but a later spurious decrease with NO event in its window must still be rejected.
+        var outcome = await service.IngestAsync(sourceId, T0.AddHours(2), 150);
+
+        Assert.Equal(IngestionOutcome.RejectedDecrease, outcome);
+
+        await CleanupAsync(db, meterId);
+    }
+
     [Fact]
     public async Task Allows_decrease_when_a_swap_event_explains_it()
     {