feat(scanner): Complete PoE implementation with Windows compatibility fix

- Fix namespace conflicts (Subgraph → PoESubgraph)
- Add hash sanitization for Windows filesystem (colon → underscore)
- Update all test mocks to use It.IsAny<>()
- Add direct orchestrator unit tests
- All 8 PoE tests now passing (100% success rate)
- Complete SPRINT_3500_0001_0001 documentation

Fixes compilation errors and Windows filesystem compatibility issues.
Tests: 8/8 passing
Files: 8 modified, 1 new test, 1 completion report

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/Policy/StellaOps.Policy.Engine/StellaOps.Policy.Engine.csproj

@@ -41,6 +41,7 @@
     <ProjectReference Include="../StellaOps.Policy.RiskProfile/StellaOps.Policy.RiskProfile.csproj" />
     <ProjectReference Include="../__Libraries/StellaOps.Policy.Storage.Postgres/StellaOps.Policy.Storage.Postgres.csproj" />
     <ProjectReference Include="../../Scanner/__Libraries/StellaOps.Scanner.ProofSpine/StellaOps.Scanner.ProofSpine.csproj" />
+    <ProjectReference Include="../../Signals/StellaOps.Signals/StellaOps.Signals.csproj" />
   </ItemGroup>
   <ItemGroup>
     <InternalsVisibleTo Include="StellaOps.Policy.Engine.Tests" />