Polish public release documentation

[Spbd1]

Motivation

• Prepare Parcel Society for an initial public GitHub release by improving documentation, contributor-facing files, and release metadata so the project is clear, reproducible, and research-oriented.
• Provide templates and placeholders (screenshots, issue/PR templates, contributing guidance, code of conduct, and changelog) to support community contributions and safe research practices.

Description

• Rewrite README.md with project description, research motivation, quick start, Docker start, demo credentials, architecture, research design, data exports, roadmap, and contributor guidance.
• Expand and finalize docs: docs/research-design.md, docs/game-mechanics.md, docs/data-dictionary.md, docs/analysis-plan.md, docs/admin-guide.md, docs/deployment.md, and docs/ethics.md for release-readiness.
• Add community and release files: CONTRIBUTING.md, CODE_OF_CONDUCT.md, CHANGELOG.md (v0.1.0), GitHub issue templates (.github/ISSUE_TEMPLATE/bug_report.md, feature_request.md, research_question.md), and a pull request template (.github/pull_request_template.md).
• Add docs/images/.gitkeep as a placeholder for release screenshots and run Prettier formatting over the edited Markdown files.

Testing

• Ran pnpm exec prettier --write README.md docs/*.md CONTRIBUTING.md CODE_OF_CONDUCT.md CHANGELOG.md .github/ISSUE_TEMPLATE/*.md .github/pull_request_template.md, which completed successfully.
• Ran git diff --check, which reported no issues.
• Attempted pnpm install, but it failed due to a registry/proxy 403 Forbidden for dependencies (blocked by environment npm registry configuration), so dependency-driven checks could not complete.
• pnpm typecheck, pnpm lint, pnpm test, and pnpm build were not able to finish because dependencies were not installed; Docker-based Compose checks also could not run because Docker is not available in the environment.

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Codex Task