semi implemented and features implemented save checkpoint

docs/features/unchecked/graph/graph-analytics-engine.md

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+# Graph Analytics Engine
+
+## Module
+Graph
+
+## Status
+IMPLEMENTED
+
+## Description
+Graph analytics with engine, pipeline, DI extensions, and Postgres persistence for analytics results.
+
+## Implementation Details
+- **Analytics engine**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphAnalyticsEngine.cs` -- core graph analytics computation engine
+- **Analytics pipeline**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphAnalyticsPipeline.cs` -- multi-stage analytics pipeline orchestration
+- **Hosted service**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphAnalyticsHostedService.cs` -- background service running analytics on schedule
+- **Analytics types**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphAnalyticsTypes.cs` -- clustering, centrality, and analytics result types
+- **Metrics**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphAnalyticsMetrics.cs` -- Prometheus-compatible analytics execution metrics
+- **Options**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphAnalyticsOptions.cs` -- configurable analytics parameters
+- **Writer options**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphAnalyticsWriterOptions.cs` -- result persistence configuration
+- **Overlay exporter**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphOverlayExporter.cs` -- exports analytics results as graph overlays
+- **In-memory writer**: `src/Graph/StellaOps.Graph.Indexer/Analytics/InMemoryGraphAnalyticsWriter.cs` -- test analytics writer
+- **In-memory snapshot**: `src/Graph/StellaOps.Graph.Indexer/Analytics/InMemoryGraphSnapshotProvider.cs` -- test snapshot provider
+- **DI extensions**: `src/Graph/StellaOps.Graph.Indexer/Analytics/GraphAnalyticsServiceCollectionExtensions.cs` -- DI registration
+- **Postgres persistence**: `src/Graph/__Libraries/StellaOps.Graph.Indexer.Persistence/Postgres/Repositories/PostgresGraphAnalyticsWriter.cs` -- PostgreSQL analytics result storage
+- **Tests**: `src/Graph/__Tests/StellaOps.Graph.Indexer.Tests/GraphAnalyticsEngineTests.cs`, `GraphAnalyticsPipelineTests.cs`, `GraphOverlayExporterTests.cs`, `GraphAnalyticsTestData.cs`
+- **Source**: Feature matrix scan
+
+## E2E Test Plan
+- [ ] Verify analytics engine computes clustering and centrality scores
+- [ ] Test pipeline executes multi-stage analytics in correct order
+- [ ] Verify hosted service runs analytics on configured schedule
+- [ ] Test Postgres persistence stores analytics results correctly
+- [ ] Verify overlay exporter generates valid overlay data from analytics