feat: Add new projects to solution and implement contract testing documentation

- Added "StellaOps.Policy.Engine", "StellaOps.Cartographer", and "StellaOps.SbomService" projects to the StellaOps solution.
- Created AGENTS.md to outline the Contract Testing Guild Charter, detailing mission, scope, and definition of done.
- Established TASKS.md for the Contract Testing Task Board, outlining tasks for Sprint 62 and Sprint 63 related to mock servers and replay testing.

src/StellaOps.Cartographer/Program.cs

@@ -0,0 +1,17 @@
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Configuration
+    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
+    .AddEnvironmentVariables("CARTOGRAPHER_");
+
+builder.Services.AddOptions();
+builder.Services.AddLogging();
+
+// TODO: register Cartographer graph builders, overlay workers, and Authority client once implementations land.
+
+var app = builder.Build();
+
+app.MapGet("/healthz", () => Results.Ok(new { status = "ok" }));
+app.MapGet("/readyz", () => Results.Ok(new { status = "warming" }));
+
+app.Run();