Update next to 16.3 and specify PNPM version in devEngines.packageManager

[nakrovati]

Pull Request

Description

1. Update Next.js to 16.3 (without updating the code) to speed up the build process, fix the PostCSS and Sharp vulnerabilities (https://npmx.dev/package/next/v/16.2.12), and reduce memory usage (https://nextjs.org/blog/next-16-3).
2. Specify the PNPM version in devEngines.packageManager in package.json, as this is a more feature-rich replacement for packageManager - https://pnpm.io/package_json#devenginespackagemanager.
3. Update PNPM to 11.11.0 due to vulnerabilities found in older versions.
4. Dedupe deps

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvements
• Security fix

Testing

• Unit tests added/updated
• Manual testing completed

pnpm test:run

Checklist

• Code follows the project's style guidelines
• Self-review completed
• TypeScript types are properly defined
• All commit messages are in English (Conventional Commits)
• All existing tests pass
• No new dependencies added, or they are justified

Related Issues

Closes #

Screenshots (if applicable)

Additional Notes