[Need support]: Sync README Demos section with the demo directory

[TKaltofen]

What and why

The README "Demos" section says "Three marimo notebooks plus two evaluation harnesses", but it then lists five notebooks, and the directory contains a third evaluation harness (eval_qa_accuracy_2hop.py) plus visual assets (circuit_schematic.html, diagram_circuit.html, diagram_layers.html) that are not listed at all. The count and the list should match what ships.

Pointers

• README.md, "Demos" section
• demo/ directory contents on main

Steps

1. Fix the opening sentence so the counts match the actual list.
2. Add the missing entries: demo/eval_qa_accuracy_2hop.py and the three HTML visual assets (one line each, like the existing semantic_field_explainer.html entry).
3. Double-check every file in demo/ (excluding demo/data/) is either listed or intentionally internal (e.g. qa_eval_lib.py as a shared library can be noted as such or skipped).

Acceptance criteria

• The Demos section count matches its list.
• Every user-facing demo file in demo/ is discoverable from the README.

Notes

This project uses semantic versioning driven by Conventional Commits, so the PR title matters: use docs: sync README demos section with demo directory.

New to the project? This issue is a good entry point, we are happy to help in the comments.

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