chore: repo scaffolding

[OranguEngineer]

Summary

• Add README.md — project pitch, stack (Django + DRF, API-first), self-hosting stub, AGPL-3.0 note, OranguStudio footer
• Add scripts/setup-labels.sh — reproducible gh label create script for type/status/priority labels
• Add .github/ISSUE_TEMPLATE/task.md and .github/pull_request_template.md
• Add CLAUDE.md — GitHub flow, branch naming, conventional commits, checkpoint commit discipline
• Add scripts/setup-main-ruleset.sh — branch ruleset script (committed for reference, not activated yet)
• Add docs/brainstorms/ and docs/plans/ — scaffolding requirements and plan

Closes #1

Notes

scripts/setup-main-ruleset.sh is not activated — run it manually as a post-merge step once this branch merges into main.

References

• Plan: docs/plans/2026-06-16-001-chore-repo-scaffolding-plan.md
• Conventional Commits: https://www.conventionalcommits.org/en/v1.0.0/
• GitHub branch rulesets: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/managing-rulesets/about-rulesets