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

src/Core/Domain/Tariff.cs

@@ -0,0 +1,30 @@
+namespace MeterVault.Core.Domain;
+
+/// <summary>
+/// A price component with a validity range (price history), scoped globally, per energy
+/// type, or per meter (SDD §5.3 <c>tariff</c>, FR-9). <see cref="ValidTo"/> null = open-ended.
+/// </summary>
+public sealed class Tariff
+{
+    public int Id { get; set; }
+
+    public TariffScope ScopeType { get; set; }
+
+    /// <summary>energy_type.id or meter.id; null for global scope.</summary>
+    public int? ScopeId { get; set; }
+
+    public TariffComponent Component { get; set; }
+
+    public double Value { get; set; }
+
+    /// <summary>e.g. 'EUR/kWh', 'EUR/m3', 'EUR/100L', 'EUR/month'.</summary>
+    public required string Unit { get; set; }
+
+    public string Currency { get; set; } = "EUR";
+
+    public DateOnly ValidFrom { get; set; }
+
+    public DateOnly? ValidTo { get; set; }
+
+    public string? Notes { get; set; }
+}