Terminology Rename, and named-graphs for explainability (#682)

Terminology Rename, and named-graphs for explainability data

Changed terminology:
  - session -> question
  - retrieval -> exploration
  - selection -> focus
  - answer -> synthesis

- uris.py: Renamed query_session_uri → question_uri,
  retrieval_uri → exploration_uri, selection_uri → focus_uri,
  answer_uri → synthesis_uri
- triples.py: Renamed corresponding triple generation functions with
  updated labels ("GraphRAG question", "Exploration", "Focus",
  "Synthesis")
- namespaces.py: Added named graph constants GRAPH_DEFAULT,
  GRAPH_SOURCE, GRAPH_RETRIEVAL
- init.py: Updated exports
- graph_rag.py: Updated to use new terminology
- invoke_graph_rag.py: Updated CLI to display new stage names
  (Question, Exploration, Focus, Synthesis)

Query-Time Explainability → Named Graph
- triples.py: Added set_graph() helper function to set named graph
  on triples
- graph_rag.py: All explainability triples now use GRAPH_RETRIEVAL
  named graph
- rag.py: Explainability triples stored in user's collection (not
  separate collection) with named graph

Extraction Provenance → Named Graph
- relationships/extract.py: Provenance triples use GRAPH_SOURCE
  named graph
- definitions/extract.py: Provenance triples use GRAPH_SOURCE
  named graph
- chunker.py: Provenance triples use GRAPH_SOURCE named graph
- pdf_decoder.py: Provenance triples use GRAPH_SOURCE named graph

CLI Updates
- show_graph.py: Added -g/--graph option to filter by named graph and
  --show-graph to display graph column

Also:
- Fix knowledge core schemas

tests/unit/test_retrieval/test_graph_rag.py

@@ -644,7 +644,7 @@ class TestQuery:
             # Verify response text
             assert response == expected_response
 
-            # Verify provenance was emitted incrementally (4 events: session, retrieval, selection, answer)
+            # Verify provenance was emitted incrementally (4 events: question, exploration, focus, synthesis)
             assert len(provenance_events) == 4
 
             # Verify each event has triples and a URN
@@ -653,11 +653,11 @@ class TestQuery:
                 assert len(triples) > 0
                 assert prov_id.startswith("urn:trustgraph:")
 
-            # Verify order: session, retrieval, selection, answer
-            assert "session" in provenance_events[0][1]
-            assert "retrieval" in provenance_events[1][1]
-            assert "selection" in provenance_events[2][1]
-            assert "answer" in provenance_events[3][1]
+            # Verify order: question, exploration, focus, synthesis
+            assert "question" in provenance_events[0][1]
+            assert "exploration" in provenance_events[1][1]
+            assert "focus" in provenance_events[2][1]
+            assert "synthesis" in provenance_events[3][1]
 
         finally:
             # Restore original methods