Add signal contracts for reachability, exploitability, trust, and unknown symbols

- Introduced `ReachabilityState`, `RuntimeHit`, `ExploitabilitySignal`, `ReachabilitySignal`, `SignalEnvelope`, `SignalType`, `TrustSignal`, and `UnknownSymbolSignal` records to define various signal types and their properties.
- Implemented JSON serialization attributes for proper data interchange.
- Created project files for the new signal contracts library and corresponding test projects.
- Added deterministic test fixtures for micro-interaction testing.
- Included cryptographic keys for secure operations with cosign.

tests/StellaOps.Gateway.WebService.Tests/GatewayHealthTests.cs

@@ -0,0 +1,27 @@
+using Microsoft.AspNetCore.Mvc.Testing;
+using Xunit;
+
+namespace StellaOps.Gateway.WebService.Tests;
+
+public class GatewayHealthTests : IClassFixture<WebApplicationFactory<Program>>
+{
+    private readonly WebApplicationFactory<Program> _factory;
+
+    public GatewayHealthTests(WebApplicationFactory<Program> factory)
+    {
+        _factory = factory;
+    }
+
+    [Fact]
+    public async Task HealthEndpoint_ReturnsOk()
+    {
+        // Arrange
+        var client = _factory.CreateClient();
+
+        // Act
+        var response = await client.GetAsync("/health");
+
+        // Assert
+        response.EnsureSuccessStatusCode();
+    }
+}

tests/StellaOps.Gateway.WebService.Tests/StellaOps.Gateway.WebService.Tests.csproj

@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <LangVersion>preview</LangVersion>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="10.0.0-rc.2.25502.107" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="xunit" Version="2.9.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.0.1">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="coverlet.collector" Version="6.0.4">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Gateway\StellaOps.Gateway.WebService\StellaOps.Gateway.WebService.csproj" />
+  </ItemGroup>
+</Project>