feat: .NET 9 contact relay (stateless minimal API)

- POST /api/contact: validate -> honeypot -> per-IP rate limit -> SMTP send
- /healthz endpoint; CORS locked to site origin; forwarded-headers for real client IP
- no persistence, no message bodies logged (IP hashed to a short non-reversible marker)
- source-generated JSON; config via env (SMTP + relay settings)
- alpine multi-stage Dockerfile, non-root, healthcheck
- verified: healthz 200, invalid 400, honeypot silent 200, missing-SMTP 502

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

relay/ContactRelay.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <InvariantGlobalization>true</InvariantGlobalization>
+    <RootNamespace>ContactRelay</RootNamespace>
+    <AssemblyName>ContactRelay</AssemblyName>
+  </PropertyGroup>
+
+</Project>