Complete batch 012 (golden set diff) and 013 (advisory chat), fix build errors

Sprints completed:
- SPRINT_20260110_012_* (golden set diff layer - 10 sprints)
- SPRINT_20260110_013_* (advisory chat - 4 sprints)

Build fixes applied:
- Fix namespace conflicts with Microsoft.Extensions.Options.Options.Create
- Fix VexDecisionReachabilityIntegrationTests API drift (major rewrite)
- Fix VexSchemaValidationTests FluentAssertions method name
- Fix FixChainGateIntegrationTests ambiguous type references
- Fix AdvisoryAI test files required properties and namespace aliases
- Add stub types for CveMappingController (ICveSymbolMappingService)
- Fix VerdictBuilderService static context issue

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/Policy/__Tests/StellaOps.Policy.Engine.Tests/Vex/VexSchemaValidationTests.cs

@@ -210,7 +210,7 @@ public sealed class VexSchemaValidationTests
         node["@id"]?.GetValue<string>().Should().StartWith("urn:uuid:");
         node["author"]?.GetValue<string>().Should().NotBeNullOrWhiteSpace();
         node["timestamp"].Should().NotBeNull();
-        node["version"]?.GetValue<int>().Should().BeGreaterOrEqualTo(1);
+        node["version"]?.GetValue<int>().Should().BeGreaterThanOrEqualTo(1);
         node["statements"].Should().NotBeNull();
     }