Quickstart (fixture)

This fixture corpus is consumed by the Phase 2 site renderer tests. To use it in a test, request the wiki_sample_graph fixture; it walks tests/fixtures/wiki_corpus/data/research/ and tests/fixtures/wiki_corpus/docs/, calls ResearchGraphExtractor.extract_file with the right source_kind per path heuristic, and merges the per-file graphs via merge_graphs.

The corpus exercises Paper, Repository, and SourceDocument code paths.