M0: scaffold solution, EF+Timescale schema, /healthz

Five-project Clean Architecture solution (Core/Infrastructure/App + Core.Tests/
Integration.Tests) on .NET 10 with central package management, snake_case EF mapping,
and shared build/style config.

- Full domain entity set + EF DbContext for the SDD §5.3 schema (singular table names).
- InitialSchema migration (relational) + TimescaleHypertables migration (raw SQL:
  create_hypertable + compression on reading, hypertable on consumption).
- App wiring: Serilog (actually wired, unlike MQTTower), DbContext, migrate-on-startup,
  /healthz. Serves plain HTTP behind a reverse proxy (no HTTPS redirect).
- deploy/Dockerfile (2-stage, ICU-capable) + docker-compose (app + timescaledb).
- Integration.Tests: shared TimescaleFixture (Testcontainers) — migrations, hypertables,
  compression policy, and /healthz all verified green (4/4).

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

tests/Integration.Tests/HealthEndpointTests.cs

@@ -0,0 +1,18 @@
+namespace MeterVault.Integration.Tests;
+
+[Collection("Timescale")]
+public sealed class HealthEndpointTests(TimescaleFixture fx)
+{
+    [Fact]
+    public async Task Healthz_returns_ok()
+    {
+        using var factory = new MeterVaultAppFactory(fx.ConnectionString);
+        using var client = factory.CreateClient();
+
+        using var response = await client.GetAsync(new Uri("/healthz", UriKind.Relative));
+
+        response.EnsureSuccessStatusCode();
+        var body = await response.Content.ReadAsStringAsync();
+        Assert.Contains("ok", body, StringComparison.OrdinalIgnoreCase);
+    }
+}