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.

src/__Libraries/StellaOps.Microservice/RouterEndpointConfig.cs

@@ -0,0 +1,24 @@
+using StellaOps.Router.Common;
+
+namespace StellaOps.Microservice;
+
+/// <summary>
+/// Configuration for a router endpoint.
+/// </summary>
+public sealed class RouterEndpointConfig
+{
+    /// <summary>
+    /// Gets or sets the router host.
+    /// </summary>
+    public required string Host { get; set; }
+
+    /// <summary>
+    /// Gets or sets the router port.
+    /// </summary>
+    public required int Port { get; set; }
+
+    /// <summary>
+    /// Gets or sets the transport type to use.
+    /// </summary>
+    public TransportType TransportType { get; set; } = TransportType.Tcp;
+}

src/__Libraries/StellaOps.Microservice/ServiceCollectionExtensions.cs

@@ -0,0 +1,28 @@
+using Microsoft.Extensions.DependencyInjection;
+
+namespace StellaOps.Microservice;
+
+/// <summary>
+/// Extension methods for registering Stella microservice services.
+/// </summary>
+public static class ServiceCollectionExtensions
+{
+    /// <summary>
+    /// Adds Stella microservice services to the service collection.
+    /// </summary>
+    /// <param name="services">The service collection.</param>
+    /// <param name="configure">Action to configure the microservice options.</param>
+    /// <returns>The service collection for chaining.</returns>
+    public static IServiceCollection AddStellaMicroservice(
+        this IServiceCollection services,
+        Action<StellaMicroserviceOptions> configure)
+    {
+        ArgumentNullException.ThrowIfNull(services);
+        ArgumentNullException.ThrowIfNull(configure);
+
+        // Stub implementation - will be filled in later sprints
+        services.Configure(configure);
+
+        return services;
+    }
+}

src/__Libraries/StellaOps.Microservice/StellaMicroserviceOptions.cs

@@ -0,0 +1,40 @@
+using StellaOps.Router.Common;
+
+namespace StellaOps.Microservice;
+
+/// <summary>
+/// Options for configuring a Stella microservice.
+/// </summary>
+public sealed class StellaMicroserviceOptions
+{
+    /// <summary>
+    /// Gets or sets the service name.
+    /// </summary>
+    public required string ServiceName { get; set; }
+
+    /// <summary>
+    /// Gets or sets the semantic version.
+    /// </summary>
+    public required string Version { get; set; }
+
+    /// <summary>
+    /// Gets or sets the region where this instance is deployed.
+    /// </summary>
+    public required string Region { get; set; }
+
+    /// <summary>
+    /// Gets or sets the unique instance identifier.
+    /// </summary>
+    public string InstanceId { get; set; } = Guid.NewGuid().ToString("N");
+
+    /// <summary>
+    /// Gets the router endpoints to connect to.
+    /// At least one router endpoint is required.
+    /// </summary>
+    public List<RouterEndpointConfig> Routers { get; set; } = [];
+
+    /// <summary>
+    /// Gets or sets the optional path to a YAML config file for endpoint overrides.
+    /// </summary>
+    public string? EndpointConfigPath { get; set; }
+}

src/__Libraries/StellaOps.Microservice/StellaOps.Microservice.csproj

@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <LangVersion>preview</LangVersion>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="10.0.0-rc.2.25502.107" />
+    <PackageReference Include="Microsoft.Extensions.Options" Version="10.0.0-rc.2.25502.107" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\StellaOps.Router.Common\StellaOps.Router.Common.csproj" />
+  </ItemGroup>
+</Project>