chore(next): align all Next apps on Next.js 16.3 #484

Context

PR #482 enables React Compiler across the apps while keeping the currently mixed Next.js versions. Before switching to the Rust compiler path, align the Next.js apps on the same Next 16.3 line.

Current versions observed in PR #482:

• apps/frontend-demo: next@^16.1.1
• apps/herbatika: next@16.1.1
• apps/n1: next@16.0.7
• apps/payload: next@16.2.3

Next.js 16.3 preview announcement: https://nextjs.org/blog/next-16-3-turbopack

Scope

• Update all Next.js apps to the same Next.js 16.3 version line.
• Prefer the stable 16.3 release if available when this ticket is picked up; use @preview only if explicitly acceptable at that point.
• Keep reactCompiler: true as-is.
• Do not enable experimental.turbopackRustReactCompiler in this PR.
• Use package-manager commands (pnpm add, pnpm update, or equivalent), not manual package.json edits.
• Keep the lockfile diff focused on this dependency alignment.

Validation

• Run changed-app lint/build/test targets locally under repo Node 24.
• Run Nx affected validation locally before pushing.
• Confirm CI passes.

Acceptance Criteria

• All Next.js apps use the same Next.js 16.3 line.
• Existing React Compiler behavior remains enabled and unchanged.
• No Rust compiler flag is introduced yet.
• CI is green.