docs: move tutorial data prompt to Hugging Face

[bobleesj]

What problem does it solve?

The copyable tutorial-data upload prompt was owned by the widget documentation even though Hugging Face owns the data format, permission metadata, validation, authentication, and Community PR workflow. This duplicated policy and created a circular link from the dataset card back to the widget repo.

What should reviewer(s) do?

Review the removal in docs/agent-prompts.md and confirm that both widget contribution pages now link directly to the dataset card Coding agents section. The full prompt is proposed in quantem-data Community PR 4; merge that data-card change first.

Verification

• npm run build passed with the reviewed paired quantem.gpu source tree.
• PYTHONPATH=src:<paired-gpu-src> pytest -q: 1,156 passed, 41 skipped, 1 existing unrelated failure in test_repository_pr_hygiene.py because main still grants issues: write.
• Markdown reference, stale-anchor, whitespace, and outgoing privacy scans passed.
• No notebook, generated HTML, scientific data, or widget source changed.

[github-actions]

• Delete bobleesj/quantem.widget:move-data-prompt-to-huggingface from its remote if you own it, it is not long-lived, and no other PR uses it.
• Remove the dedicated worktree and local move-data-prompt-to-huggingface branch after confirming the worktree is clean.
• Fetch electronmicroscopy/quantem.widget and update local main before starting new work.