QUE-373: Rebuild the Set-of-Mark engineering reference on a real page

The reference now walks page 5 of the KREF 2Q'26 deck through every stage
of the table extractor. Its figures come from that document's extraction by
commit d54559d: the gridded image the locator saw, the model's raw answer,
the geometry chain replayed to the exact som_region, the correction agent's
crop and tagged grid, all 38 cell rectangles on the balance sheet, the
content_region cut, and the call timeline from the run's LangSmith traces.

Every claim was re-verified against current main. Corrections carried in:
dependency versions (pydantic-ai-slim and pydantic-graph 2.47.0),
llm_corrected semantics, the value check's page-wide scope, the title
printed-text check, and the four open limitations. Deprecated modules are no
longer named. Prose was edited to the textbook plugin's rules and checked by
a reader with no project context.

The build uses the textbook plugin's stylesheet. The page images are
force-added because *.png is ignored repo-wide.