docs: add LEARNINGS.md and PR template for AI agent guidance

[Copilot]

No structured way existed for AI agents to learn from past PRs or produce consistent PR descriptions. Adds a living learnings log and a GitHub PR template to close both gaps.

Summary

docs/LEARNINGS.md gives agents a categorised reference of 28 lessons extracted from PRs #54–#94 (mobile/CSS quirks, build system rules, test reliability, architecture boundaries, security, feature design, release flow) plus a per-PR log with Problem/Approach/Learning/Key-files entries. .github/pull_request_template.md enforces a uniform Summary → Changes → Agent Checklist structure on every PR going forward. AGENTS.md is updated to surface both documents immediately and adds a "must add learning entry" rule to the session-end requirements.

Changes

• docs/LEARNINGS.md — PR entry template, PR description template, 28-rule categorised learnings tables, pre-populated PR log (feat: add JSDoc + checkJs TypeScript type checking (Option B) #54–docs: add Phase 3 PRDs — 8 satirical engagement features #94)
• .github/pull_request_template.md — Summary, Changes checklist, 10-item Agent Checklist (including learning-entry requirement)
• AGENTS.md — companion-document table at top, new "Documenting PR learnings" subsection, new "What NOT to Do" rule

Agent Checklist

• npm run test:ci passes (all unit tests green, coverage not decreased)
• npm run build && npm run test:e2e passes (all E2E tests green)
• No generated files committed (script.js, styles.css, *-data.js)
• All dynamic innerHTML values pass through escHtml()
• No DOM references introduced in death-clock-core.js
• No new runtime npm packages added
• GitHub Actions uses: pins use a full commit SHA + inline semver comment
• PR title follows Conventional Commits (feat:, fix:, docs:, chore:, etc.)
• project-stats.yaml updated if this session merges one or more PRs
• Relevant entry added to docs/LEARNINGS.md (new pattern or lesson learned)

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 4ca8ba65-e9c6-4cf0-88d5-a4049f754da6

📥 Commits

Reviewing files that changed from the base of the PR and between 2442787 and b2adf12.

📒 Files selected for processing (3)

• .github/pull_request_template.md
• AGENTS.md
• docs/LEARNINGS.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch copilot/create-learning-document-structure

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[github-actions]

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