Improve website accessibility controls

[daxia778]

Summary

• adds a proper text equivalent for the animated 4D banana canvas with labelled/described relationships, fallback canvas text, and static frame descriptions
• adds a pause/resume control with live status plus a reduced-motion static-frame path
• adds visible focus treatment and an accessibility audit note for the website
• ships the existing logo SVG inside docs/ so the published site root resolves the brand image

Addresses #149.

Validation

• node --check docs/banana4d.js
• parsed docs/index.html with Python html.parser
• git diff --check
• curl -I http://127.0.0.1:8765/ and /logo.svg both return 200 from docs/
• local browser smoke test at http://127.0.0.1:8765/: desktop 1280x720 and mobile 390x844, no console errors/warnings, logo loads, motion control state updates correctly

Payout, if awarded: USDC on Base to 0xB54Ec1F0905186553FaB1763409e1CC127b874F9

[daxia778]

Follow-up commit ef842c8 adds dependency-free docs accessibility contract tests for the website patch. The new test file verifies the banana canvas text equivalent resolves to real IDs, fallback canvas text remains present, the pause/resume control is a real button with live status, the skip link targets the main landmark, and the reduced-motion/focus-visible hooks stay in place.\n\nValidation after the update:\n- python3 -m pytest src/test_docs_accessibility.py -q → 4 passed\n- node --check docs/banana4d.js\n- python3 -m py_compile src/test_docs_accessibility.py\n- git diff --check -- docs/index.html docs/banana4d.js docs/styles.css src/test_docs_accessibility.py