feat: .env UI editor

[royendo]

Copy paste and Claude Code the UI editor from RC to RD.
Not sure what the folder arch is but .env editor is in web-admin/ and copied to web-common/ for RD. Since its pretty much a replica, can point it to the same file to reduce code dupe but they are slight different spaces so wanted to do them separately on first pass.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[royendo]

where to consolidate utils?
web-common/src/features/environment-variables/utils.ts
and
web-admin/src/features/projects/environment-variables/utils.ts

have the same functions and lots of repeat since they are the same functionality

[royendo]

Before Deploy:

After Deploy:

Code view Before Deploy:

[royendo]

@begelundmuller , based on Mike's requests to add push-pull button in the UI here: https://rilldata.slack.com/archives/C01A9DYP013/p1765989576246559?thread_ts=1765901488.470909&cid=C01A9DYP013

required some new backend changes, so tagging you as a reviewer for this PR, as well.

If this is "too complicated" or adds brittleness to the code base, we can remove the backend changes and buttons for this PR and tackle it in a dedicated PR in the future.

Thoughts?

[begelundmuller]

The backend code here seems correct at a high level, although it could do with some cleaning up (there are some anti-patterns and no tests)