Review request: baseline toolchain setup

Summary

Baseline toolchain setup is complete. All validation commands pass. Requesting review.

Changes

Commit: 4106c64 on master branch

Functional changes

1. src/test/setup.ts — Added cleanup() in afterEach to prevent DOM leaking between tests. Without this, the second test found duplicate elements from the first test's render.
2. tsconfig.json — Next.js build auto-updated jsx from preserve to react-jsx and added .next/dev/types/**/*.ts to include. These are standard Next.js requirements.
3. package.json / package-lock.json — Next.js build auto-installed @types/node as a devDependency.

Formatting changes

4. 42 files — Prettier formatting applied (whitespace, trailing newlines, list spacing).

Validation results

All commands pass:

• npm run typecheck — OK
• npm run lint — OK
• npm test — 2/2 tests pass
• npm run format:check — OK
• npm run build — OK (static pages generated)

Review focus areas

• Test setup cleanup approach (explicit afterEach + cleanup())
• tsconfig.json changes from Next.js auto-config are acceptable
• Prettier formatting did not break any memo YAML frontmatter
• Note: docs/architecture.md says "ESLint 10" but installed version is ESLint 9.39.2 (package.json specifies ^9.39.2). This is a pre-existing inaccuracy from the planner's plan — flagging for awareness.

Acceptance criteria checklist

• All config files created as specified by planner
• All dependencies installed
• All docs updated with exact content
• Local validation passes (lint/test/build/typecheck/format)
• Review request sent to reviewer
• Status update sent to project manager