Add .env to .gitignore

Currently the `.gitignore` file of the project does not include the broadly used `.env` across the majority of projects.

Users might be unaware of this and push sensitive information potentially putting funds and access control at risk.

Add `.env` to the `.gitignore` on this and any other template you offer where it might be missing.

Inspect the repository's .gitignore and any other template files offered by the project, checking whether .env is already excluded. Add the missing ignore entry wherever needed, then verify the diff shows the intended templates protect environment files without unrelated changes.

Written by the indexing model from the issue text.