F2-AI-Inc

Add a deterministic PDF test fixture via gen_fixtures.rs with hand-computed expected geometry. Use when a new feature or bug fix needs a PDF exercising specific structure (fonts, forms, rotation, images, annotations, malformed content).

Regenerate golden JSON test files the only correct way — on Linux via Docker, since goldens are Linux-canonical (platform font substitution shifts glyph metrics across OSes). Use when an intended behavior change makes golden tests fail, or after adding a fixture.

Visually verify extraction changes against real PDFs using the embedded playground before opening a PR. Use after any change to extraction geometry, grouping, granularity shapes, or the playground itself.