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>

docs2/api/overview.md

@@ -0,0 +1,20 @@
+# API overview
+
+## Conventions
+- JSON payloads use camelCase and RFC 7807 for problem details.
+- Streaming endpoints support SSE or NDJSON.
+- Timestamps are UTC ISO 8601.
+
+## Major API groups
+- Scanner: scan submission, status, SBOM retrieval, diffs, reports.
+- Policy: policy import/export, validation, preview, and simulation.
+- Scheduler: schedules, runs, and impact selection.
+- Notify: rules, channels, deliveries, and test sends.
+- VEX and consensus: consensus evaluation and exports.
+- Signals: reachability, runtime facts, unknowns.
+- Export Center: export runs and offline bundles.
+- Authority: token issuance and administrative endpoints.
+
+## Contracts and schemas
+- OpenAPI specs live under docs/api/.
+- JSON schemas live under docs/schemas/ and docs/contracts/.