Subgraph provenance (#694)

Replace per-triple provenance reification with subgraph model

Extraction provenance previously created a full reification (statement
URI, activity, agent) for every single extracted triple, producing ~13
provenance triples per knowledge triple.  Since each chunk is processed
by a single LLM call, this was both redundant and semantically
inaccurate.

Now one subgraph object is created per chunk extraction, with
tg:contains linking to each extracted triple.  For 20 extractions from
a chunk this reduces provenance from ~260 triples to ~33.

- Rename tg:reifies -> tg:contains, stmt_uri -> subgraph_uri
- Replace triple_provenance_triples() with subgraph_provenance_triples()
- Refactor kg-extract-definitions and kg-extract-relationships to
  generate provenance once per chunk instead of per triple
- Add subgraph provenance to kg-extract-ontology and kg-extract-agent
  (previously had none)
- Update CLI tools and tech specs to match

Also rename tg-show-document-hierarchy to tg-show-extraction-provenance.

Added extra typing for extraction provenance, fixed extraction prov CLI

trustgraph-base/trustgraph/provenance/namespaces.py

@@ -42,7 +42,7 @@ SKOS_DEFINITION = SKOS + "definition"
 
 # TrustGraph namespace for custom predicates
 TG = "https://trustgraph.ai/ns/"
-TG_REIFIES = TG + "reifies"
+TG_CONTAINS = TG + "contains"
 TG_PAGE_COUNT = TG + "pageCount"
 TG_MIME_TYPE = TG + "mimeType"
 TG_PAGE_NUMBER = TG + "pageNumber"
@@ -72,6 +72,12 @@ TG_DOCUMENT = TG + "document"  # Reference to document in librarian
 TG_CHUNK_COUNT = TG + "chunkCount"
 TG_SELECTED_CHUNK = TG + "selectedChunk"
 
+# Extraction provenance entity types
+TG_DOCUMENT_TYPE = TG + "Document"
+TG_PAGE_TYPE = TG + "Page"
+TG_CHUNK_TYPE = TG + "Chunk"
+TG_SUBGRAPH_TYPE = TG + "Subgraph"
+
 # Explainability entity types (shared)
 TG_QUESTION = TG + "Question"
 TG_EXPLORATION = TG + "Exploration"