feat: filter and cap GraphRAG reranker input across full stack (#1021)

- Filter out RDF/RDFS/OWL schema predicates (rdfs:domain, owl:inverseOf,
  etc.) from hop traversal, keeping rdf:type for data signal
- Skip edges where reranker-visible components are unlabeled IRIs, since
  the cross-encoder cannot meaningfully score raw URIs
- Add max-reranker-input safety cap (default 350) to prevent overloading
  the reranker, applied after filtering for maximum useful candidates
- Expose max-reranker-input as per-request parameter through schema,
  translator, REST API, socket client, CLI, and OpenAPI spec
- Update tests
- Update tech spec

specs/api/components/schemas/rag/GraphRagRequest.yaml

@@ -42,6 +42,13 @@ properties:
     minimum: 1
     maximum: 5
     example: 3
+  max-reranker-input:
+    type: integer
+    description: Maximum candidate edges sent to the reranker per hop
+    default: 350
+    minimum: 1
+    maximum: 1000
+    example: 350
   streaming:
     type: boolean
     description: Enable streaming response delivery