Resolve extractor redundancy + unused L2 META

[StigNorland]

llm_extractor.py (triple extraction) is shadowed by the direct _extract_concepts_llm path in context.py, which wins. The L2 META node level is declared but never used.

• Decide whether to keep, wire in, or remove the triple extractor
• Decide whether L2 META has a near-term purpose or should be dropped

Refs: src/library/llm_extractor.py, src/library/context.py:945 (_extract_concepts), src/library/graph.py:38 (NodeLevel.META)

[StigNorland]

Addressed by the v2 graph design (#18): L2 META gets a real job as the bottom-up concept/community tier formed from entity-relationship clusters (doc §6). The redundant triple extractor question stays here. Tracking the META part under #18.

[StigNorland]

Expanded scope. src/library/concept_extractor.py is a stale duplicate of an older context.py (Turn/BackingStore/ContextAssembler), not a concept extractor. The spaCy-triple extract_concepts that context.py / llm_extractor.py import does not exist → the entire spaCy fallback path is dead (but guarded). Cleanup: delete the stale module + remove dead _EXTRACTOR_AVAILABLE/_spacy_extract branches. Best done as part of the v2 extraction rewrite (#18) since that replaces this layer wholesale.