New graph_export.py module supporting the `markitect infospace graph`
command added in the previous commit.
- build_entity_graph(): constructs node/edge graph from L2 classifications
and L3 relation triplets, with feedback loop detection via networkx
- apply_filters(): subgraph filters by entity type, VSM system, ego
neighbourhood, feedback-loops-only, and classified-only
- to_mermaid(): Mermaid flowchart export
- Uses "-- label -->" syntax for all edges (robust with parentheses);
"== label ==>" thick arrows for feedback loop edges
- markdown_fence=True wraps output in ```mermaid block (VS Code / GitHub)
- color_by="type" or "vsm" with distinct palettes for each
- to_dot(): Graphviz DOT export with fillcolor per type/VSM system
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
