fix: Updated next to v16

[cs-raj]

Upgrade Next.js from 15.5.9 to 16.x

Summary

Upgrades Next.js to v16 to address security vulnerabilities and align with the latest framework version. This upgrade includes breaking changes that have been addressed to maintain current behavior.

Changes

Dependencies

• next: 15.5.9 → ^16
• eslint-config-next: ^15 → ^16
• react/react-dom: Updated to ^19.2.4 (compatible with Next.js 16)

Configuration Updates

Image Configuration (next.config.mjs)

• Added minimumCacheTTL: 60 to preserve existing cache behavior (Next.js 16 defaults to 4 hours)
• Existing remotePatterns configuration maintained

ESLint Migration

• Migrated from legacy .eslintrc.json to flat config format (eslint.config.mjs)
• Updated lint script: "next lint" → "eslint . --ext .ts,.tsx" (Next.js 16 removed next lint command)
• Preserved existing rule overrides (@typescript-eslint/no-explicit-any: off)

Breaking Changes Addressed

1. next lint removal: Replaced with direct ESLint CLI usage
2. ESLint flat config: Migrated to eslint.config.mjs (required for Next.js 16 / ESLint 9+)
3. Image cache TTL: Explicitly set to 60s to match previous default behavior

Verification

• ✅ Lint passes with new flat config
• ✅ Build compiles successfully (Next.js 16.1.6 with Turbopack)
• ✅ No application code changes required (Pages Router compatibility maintained)

Notes

• Node.js 20.9+ required (already satisfied in current environment)
• Turbopack is now default for next dev and next build (no script changes needed)
• Build will require Contentstack environment variables to be set (unchanged behavior)

References

• Next.js 16 Upgrade Guide
• Next.js 16 ESLint Setup