Ability to Copy-and-Paste .env

### What problem are you trying to solve?

I have to input each individual project level environment variable into the Deploy UI.

### Describe the solution you'd like

Ideally I'd like to be able to copy my env file, into a text box and just click 'Add' then all the environment variables would be set.
Or use cli.

### Describe alternatives you've considered

Tried to use deploycli but it no longer seems to support deploycli secrets.

### Documentation, Adoption, Migration Strategy

_No response_

No implementation files or tests are named. Start by tracing the Deploy UI environment-variable flow and the deploycli secrets entry point; establish how .env input should be parsed and validated, then verify that both interfaces set the requested project variables consistently.

Written by the indexing model from the issue text.