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/TimescaleFixture.cs

@@ -0,0 +1,45 @@
+using MeterVault.Infrastructure.Persistence;
+using Microsoft.EntityFrameworkCore;
+using Testcontainers.PostgreSql;
+
+namespace MeterVault.Integration.Tests;
+
+/// <summary>
+/// Spins up exactly one TimescaleDB container per test run (shared via the "Timescale"
+/// collection) and applies migrations once. Tests reuse it and isolate themselves with Respawn.
+/// The image tag is pinned: the compression DDL (add_compression_policy) was renamed toward
+/// add_columnstore_policy in newer Timescale, so a floating tag would risk breaking migrations.
+/// </summary>
+public sealed class TimescaleFixture : IAsyncLifetime
+{
+    private readonly PostgreSqlContainer _db = new PostgreSqlBuilder("timescale/timescaledb:2.17.2-pg16")
+        .WithDatabase("metervault")
+        .WithUsername("metervault")
+        .WithPassword("metervault")
+        .Build();
+
+    public string ConnectionString => _db.GetConnectionString();
+
+    public MeterVaultDbContext CreateContext()
+    {
+        var options = new DbContextOptionsBuilder<MeterVaultDbContext>()
+            .UseNpgsql(ConnectionString, npgsql =>
+                npgsql.MigrationsAssembly(typeof(MeterVaultDbContext).Assembly.FullName))
+            .UseSnakeCaseNamingConvention()
+            .Options;
+        return new MeterVaultDbContext(options);
+    }
+
+    public async Task InitializeAsync()
+    {
+        await _db.StartAsync();
+        await using var ctx = CreateContext();
+        await ctx.Database.MigrateAsync();
+    }
+
+    public async Task DisposeAsync() => await _db.DisposeAsync();
+}
+
+/// <summary>Binds the shared <see cref="TimescaleFixture"/> to all tests in the "Timescale" collection.</summary>
+[CollectionDefinition("Timescale")]
+public sealed class TimescaleCollection : ICollectionFixture<TimescaleFixture>;