feat(browser): enforce verify row shape

[jackwener]

Summary

• add verify row-shape validation for compact agent-native rows
• fail browser verify before fixture handling when rows exceed 12 top-level keys, nest deeper than one level, or hide id-shaped fields under nested objects
• document the shape rules in English and Chinese extending guides

Verification

• npm run typecheck
• npx vitest run src/browser/verify-fixture.test.ts src/cli.test.ts --project unit
• npm run build
• npm run check:silent-column-drop
• npm run check:typed-error-lint
• npm run docs:build