Instance-wide default Nixpacks settings (e.g., Node 22) for all new projects/apps

What problem will this feature address?

There is no instance-wide Nixpacks runtime default. I must repeat NIXPACKS_NODE_VERSION per project/app, which causes drift and occasional build failures.

Describe the solution you'd like

Add an Instance Settings → Build defaults panel to define Nixpacks env key-values applied to every newly created project/app by default. Support inheritance and overrides (instance < project < app). Expose via API/CLI.

Describe alternatives you've considered

Project shared variables, templates, dokploy env push, repo .nixpacks.toml or package.json engines. These help but are not a true global default.

Additional context

Real case: Next.js 15 needs Node ≥20. Vercel uses Node 22. Dokploy default picks Node 18, leading to toSorted is not a function during build. A global NIXPACKS_NODE_VERSION=22 default would prevent this across teams.

Will you send a PR to implement it?

No

Start by tracing the existing Instance Settings flow and the project/app creation paths, then inspect the current API and CLI entry points for environment settings. Done means a Build defaults panel can define Nixpacks key-values for new projects and apps, with instance < project < app inheritance and overrides exposed through both API and CLI.