CLI - Make it harder to accidentally use a server-issued login

[bfops]

Description of Changes

Motivated by #6145.

We have several CLI commands that 1) ask the user whether they want to log in with spacetimedb.com, and 2) automatically use a server-issued login if the user passed --yes.

This PR updates the behavior so that 1) we print a warning and ask the user if they're super-sure, and 2) reject --yes if the user is not logged in.

This is to minimize the poor-UX situations where users end up with a "split identity" between their local DB and maincloud, where they end up trying to juggle multiple identities. The intended behavior is (and has been for a while) that users use the spacetimedb.com login on all servers.

Reverts #6116.

API and ABI breaking changes

This changes the behavior of spacetime --yes for any commands that used to ask whether you wanted a server-issued-login.

Rollback safety impact

n/a

Expected complexity level and risk

1

Testing

• Added smoketests for both changes in behavior
• updated existing smoketests to login properly under the new regime

Simplified the Core login smoketests to check for WARNING instead of matching prompt wording, and for only You are not logged in on stderr when rejecting --yes.