docs: add pull request release checklist

.github/PULL_REQUEST_TEMPLATE.md

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+## Summary
+
+<!-- What changed, and why? Keep this focused on user/business impact. -->
+
+## Scope
+
+- [ ] UI / product behavior
+- [ ] API / backend logic
+- [ ] Settings / admin configuration
+- [ ] Performance / caching
+- [ ] Logging / security
+- [ ] Documentation / CI / repository hygiene
+
+## Required Verification
+
+- [ ] `pnpm check:quality`
+- [ ] `AUTH_TRUST_HOST=true PORT=3001 pnpm dev`
+- [ ] `SMOKE_BASE_URL=http://127.0.0.1:3001 pnpm smoke:routes`
+
+If any required check was not run, explain why:
+
+```text
+
+```
+
+## Release Readiness
+
+- [ ] No real secrets, OAuth codes, cookies, Authorization headers, signed URLs, or `.env.local` values are included.
+- [ ] No tracked local artifacts such as `.DS_Store`, swap files, `.claude/`, migration backups, or `tsconfig.tsbuildinfo`.
+- [ ] No new public UI links point to `/classic` or `/chat/[id]`.
+- [ ] `/api/chat` remains treated as an internal Canvas/Agent generation API unless this PR explicitly migrates callers.
+- [ ] New or modified high-risk logging uses `createLogger` / `createClientLogger` and is covered by `pnpm check:logs` when applicable.
+
+## Screenshots / Evidence
+
+<!-- Add screenshots, route smoke output, CI links, or notes for reviewers. -->
+
+## Follow-ups
+
+<!-- List intentional non-blocking follow-ups, if any. -->