Polish rill login with better hints and interactive handling

[begelundmuller]

• Removes the unused --org flag from rill auth login
• Ensures correct (non)interative handling
• Cleans up log messages

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!

[pjain1]

nit:so no way to directly choose a default org in non interactive way, may be they just run org switch if needed.

[begelundmuller]

nit:so no way to directly choose a default org in non interactive way, may be they just run org switch if needed.

Yup, if needed in non-interactive mode, they can run rill org switch separately (it prints a hint about it as part of rill login).