[jarrad]

Summary

• Remove the CLI login fallback that treated duplicate-looking error text as a successful existing-account login.
• Call LoginStore.CreateUser directly and continue to /api/me only after a successful account API response.
• Remove the unused CreateNewUser (bool, error) helper. Its sole caller discarded the boolean, and a successful HTTP 201 cannot distinguish a new account from one brev-deploy recovered for the same token.

Account contract and rollout

The live CLI calls brev-deploy POST /api/users, not dev-plane directly. BREV-13201 makes brev-deploy consume dev-plane AlreadyExists, resolve only the account owned by the supplied token, and return HTTP 201. A username collision with no account for that token remains an error. There is no public duplicate-account code for the CLI to consume, so the old false, nil text-match path is obsolete.

Deploy BREV-13201's dev-plane producer first, then its brev-deploy bridge, before releasing this CLI change. This PR targets brev-cli main and does not depend on generic CLI parser PR #515.

Proof

• Red on baseline: uncoded_collision_text incorrectly continued to /api/me.
• Green: go test ./pkg/cmd/login -count=1 after both commits.
• On current head 8f07a09a, build, format, lint, vet, CodeQL, CLI output compatibility, and full repository tests passed. GitHub's release-test steps and workflow report success, though the job/check record remains in_progress at the time of this update.
• git diff --check passed and the worktree is clean.

Issue: https://linear.app/nvidia/issue/BREV-13200/replace-duplicate-user-text-matching-in-brev-cli-login