refactor(graph): absorb Cartographer into graph-api + wire Graph Indexer

- Wire Graph Indexer library + Persistence into graph-api (csproj refs + DI)
- Add build/overlay endpoints matching Scheduler HTTP contracts
  (POST/GET /api/graphs/builds, POST/GET /api/graphs/overlays)
- Add PostgresGraphRepository for reading from graph.graph_nodes/edges
- Register SBOM ingest, analytics, change-stream, and inspector pipelines
- Comment out Cartographer container in compose (empty shell, Slot 21)
- Add cartographer.stella-ops.local as backwards-compat alias on graph-api
- Update Scheduler config to target graph.stella-ops.local
- Update services-matrix.env, hosts file, port-registry, module-matrix
- Update component-map, architecture docs, Scanner/Graph READMEs
- Eliminates 1 container (stellaops-cartographer)

All 133 existing tests pass (77 Api + 37 Indexer + 19 Core).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

devops/compose/hosts.stellaops.local

@@ -27,7 +27,8 @@
 # 127.1.0.18 taskrunner.stella-ops.local  # REMOVED: TaskRunner service deleted
 127.1.0.19 scheduler.stella-ops.local
 127.1.0.20 graph.stella-ops.local
-127.1.0.21 cartographer.stella-ops.local
+# 127.1.0.21 cartographer.stella-ops.local  # RETIRED: merged into graph-api (Slot 20)
+127.1.0.20 cartographer.stella-ops.local
 127.1.0.22 reachgraph.stella-ops.local
 127.1.0.23 timelineindexer.stella-ops.local
 127.1.0.24 timeline.stella-ops.local