fix: generate supported Next.js lint setup

[rogerchappel]

Summary

• replace the removed next lint command with the ESLint CLI
• generate a Next.js flat ESLint configuration and required dependency
• install, lint, and run repository validation for the generated Next app in smoke coverage

Commits

• fix: generate supported Next.js lint setup

Verification

• pnpm install --frozen-lockfile
• pnpm run release:check
• git diff --check

The smoke check resolved Next.js 16.2.11, ran npm run lint, and completed bash scripts/validate.sh, including next build.