Declare the Node version dAppBooster needs #484

User story / Problem statement

Currently dAppBooster declares no engines field. The only hint at a Node version is .nvmrc, which nothing reads at install time. A user, or the installer that scaffolds this template, has no way to know which Node it needs.

Expected outcome

dAppBooster states its Node requirement in package.json, matching the version canton-dappbooster requires. A user on an older Node is told up front instead of hitting a confusing failure later.

Acceptance criteria

• package.json declares engines.node as >=24.15.0
• .nvmrc names the same version
• Starting the project on an older Node reports the requirement
• CI runs on that version

Technical notes

The dAppBooster installer checks a per-stack minNodeVersion before cloning. canton-dappbooster declares 24.15.0; this repo declares nothing, so EVM users get no check at all. The aim is one shared Node version across the installer, this repo and canton-dappbooster, so future drift is visible.