Add Policy DSL Validator, Schema Exporter, and Simulation Smoke tools

- Implemented PolicyDslValidator with command-line options for strict mode and JSON output.
- Created PolicySchemaExporter to generate JSON schemas for policy-related models.
- Developed PolicySimulationSmoke tool to validate policy simulations against expected outcomes.
- Added project files and necessary dependencies for each tool.
- Ensured proper error handling and usage instructions across tools.

src/StellaOps.Authority/StellaOps.Auth.Abstractions/StellaOpsServiceIdentities.cs

@@ -0,0 +1,17 @@
+namespace StellaOps.Auth.Abstractions;
+
+/// <summary>
+/// Canonical identifiers for StellaOps service principals.
+/// </summary>
+public static class StellaOpsServiceIdentities
+{
+    /// <summary>
+    /// Service identity used by Policy Engine when materialising effective findings.
+    /// </summary>
+    public const string PolicyEngine = "policy-engine";
+
+    /// <summary>
+    /// Service identity used by Cartographer when constructing and maintaining graph projections.
+    /// </summary>
+    public const string Cartographer = "cartographer";
+}