feat(infospace): add L3 relation graph with VSM-aware triplets (S2.8)

Implements the L3 relation graph layer — a directed graph of (Subject,
Predicate, Object) triplets annotated with VSM channel codes and feedback
roles. Triplets are authored as markdown files under output/relations/,
parsed into RelationMeta dataclasses, and analysed with networkx.

New modules:
- markitect/infospace/relation_models.py — RelationMeta dataclass +
  RELATION_TYPES controlled vocabulary (15 relation classes → VSM codes)
- markitect/infospace/relation_parser.py — parse_relation_file() and
  parse_relations_directory()

New schema: examples/infospace-with-history/schemas/relation-schema-v1.0.md
  — file naming convention, required sections, controlled vocabulary table

15 seed relation files covering the three core WoN feedback loops:
  - Capital Accumulation loop (positive reinforcement, S1/S3)
  - Market Price Balancing loop (negative feedback, S2/S3)
  - Market Extent mutual dependency (S1/S2)
  Plus structural relations: wages regulation, rent residual, price
  decomposition, invisible hand coordination

CLI: markitect infospace relations [--entity SLUG] [--vsm FILTER]
     [--loops] [--stats]
  - Builds directed graph from parsed files
  - Detects feedback loops via nx.simple_cycles()
  - 6 loops found from 15 seed relations (3 intended + 3 emergent)
  - --stats aggregates by VSM system code (strips parentheticals)

Config: InfospaceConfig gains relations_dir (default output/relations)
infospace.yaml: schemas.relation references relation-schema-v1.0.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/infospace-with-history/infospace.yaml

@@ -17,6 +17,7 @@ schemas:
   entity: schemas/economic-entity-schema-v1.0.md
   mapping: schemas/vsm-mapping-schema-v1.0.md
   analysis: schemas/chapter-analysis-schema-v1.0.md
+  relation: schemas/relation-schema-v1.0.md
 
 competency_questions: |
   1. How does Smith's division of labour map to VSM System 1 operations?