Reuse existing SSO auth sessions

[cloudsmith-iduffy]

Summary

• reuse renewable SSO sessions before prompting for a Workspace or opening a browser
• report session status and access-token expiry in human-readable and structured output
• repurpose --force to explicitly select browser authentication

Validation

• pytest -q cloudsmith_cli/cli/tests/commands/test_auth.py
• pre-commit run --files cloudsmith_cli/cli/commands/auth.py cloudsmith_cli/cli/tests/commands/test_auth.py CHANGELOG.md
• git diff --check

Draft top layer above #408. Stack metadata will be updated separately after verification.