docs: add contributor and scenario guidance

[bnquon]

Summary

This PR gives Orson a clearer contributor and scenario-documentation surface as the project moves beyond its initial MVP planning phase.

What changed

• Replaced the original milestone-heavy roadmap with a concise directional roadmap. It explicitly states that priorities are flexible and not strictly followed.
• Added CONTRIBUTING.md with local setup, demo Kafka instructions, scenario guidelines, branch conventions, validation commands, and PR expectations.
• Added a canonical scenario-format guide and scenario examples index, while keeping scenarios/order-flow.yaml as the complete bundled example.
• Added a PR template without a checklist.
• Added structured GitHub bug-report and feature-request forms.
• Added a Scenario Browser info button with an accessible YAML guide modal and copyable compact example.
• Tightened README links so the new documentation is discoverable.

User-facing behavior

Users can open the scenario guide from the Scenario Browser header to understand the YAML structure, watched topics, topology edges, and correlation settings. They can copy a valid compact example without leaving the app.

Validation

• npm run check
• npm run test:frontend
• npm --prefix frontend run build
• git diff --check

Notes

The modal intentionally does not include an Open example action. The full canonical example remains in scenarios/order-flow.yaml, with the detailed reference in docs/scenario-format.md.

[pullfrog]

Important

Please correct the contributor prerequisite and the scenario guide's topology contract before merging.

Reviewed changes This review covers the contributor and scenario documentation, repository templates, README and roadmap updates, Scenario Browser guide modal, styling, and interaction tests.

• Contributor guidance — Reviewed local setup, demo startup, validation commands, branch conventions, and pull request expectations.
• Scenario guidance — Reviewed the YAML format reference, bundled examples index, and modal's copyable example.
• Scenario Browser guide — Reviewed the new trigger, modal behavior, styling, accessibility attributes, and frontend tests.

  ^{｜ Fix all ➔ ｜ Fix 👍s ➔ ｜ View workflow run ｜ Using GPT Luna ｜ 𝕏}

[pullfrog]

ℹ️ No new issues found in this incremental delta. The prior review findings remain open.

Reviewed changes This incremental review covers the repository ownership configuration added since the prior Pullfrog review.

• Repository ownership — Added a wildcard .github/CODEOWNERS rule assigning the default owner for repository changes.

  ^{｜ Fix it ➔ ｜ View workflow run ｜ Using GPT Luna ｜ 𝕏}

[pullfrog]

✅ No new issues found.

Reviewed changes This incremental review covers the setup and topology guidance changes since the prior Pullfrog review.

• Clarified prerequisites — Documented Node.js 20.19+ or 22.12+, matching the locked frontend toolchain.
• Corrected topology guidance — Explained that disconnected watched-topic components remain capturable while only connected topics appear connected to the root graph.
• Updated interaction coverage — Adjusted the Scenario Browser guide assertions to reflect the clarified topology contract.

  ^{｜ View workflow run ｜ Using GPT Luna ｜ 𝕏}