Improve project documentation

[maveryn]

Summary

• lead the repository and project-page heroes with the verified 24-benchmark transfer result
• reduce top-level resource clutter, keep the runnable quickstart prominent, and collapse the full 24-row table behind an expander
• add a deterministic 1280×640 social-preview generator and committed PNG, and use it for website Open Graph/Twitter metadata
• link Issues and Discussions from contributor surfaces
• extend visibility/site tests for the new public contracts

Public metadata already updated

• put the interactive Space first in the Hugging Face collection
• added a streaming example to the dataset card (commit)
• added the verified montage reference answer—without claiming an unrecorded model generation—to the 3B card and 7B card
• expanded repository topics, enabled Discussions, and opened scoped issues #3, #4, #5, and #6

Validation

• python -m pytest -q tests/test_docs_site.py tests/test_public_paper.py tests/test_visibility_surfaces.py — 25 passed
• mkdocs build --strict --site-dir site — passed
• repository hygiene scan — passed
• social preview regenerated twice under the pinned rendering stack with identical SHA-256 573555b084a6e9e84a6b9d9c516bc2db2f10305acca49c65d7c2688a57913c40

The full Windows test suite was not run to completion: its first failure is the existing symlink-privilege test (WinError 1314), while CI runs on Ubuntu.

Manual repository-setting follow-up

GitHub does not expose social-preview upload through its supported repository API. After review, upload docs/assets/social/trace-social-preview.png under Settings → Social preview; the website metadata already points to the committed asset.