[codex] Add README quick demo assets

[kymuco]

Summary

• Added a compact Quick demo section near the top of README.md.
• Added a small curated synthetic/generated demo bundle under docs/assets/demo/.
• Included one SVG preview, four short OGG audio examples, and two generated Markdown artifacts.

Notes

• This is a docs/demo-assets update only.
• Demo assets are synthetic/generated from the evaluation showcase workflow.
• Approximate added demo asset size: 40,635 bytes (~39.7 KiB).
• No scoring, alignment, preprocessing, CLI/API contracts, or report schemas were changed.
• GitHub CI should be awaited separately.

Validation

• ruff check . passed.
• python -m build passed.
• pytest tests initially failed before install because practicelens was not importable; after python -m pip install -e .[dev], pytest tests completed with 93 passed and 3 failed. The failures are existing Windows path-separator behavior (out/session expected vs out\session actual) and are intentionally not fixed in this docs-only PR.