feat: add login command, alphabetize help, remove workflows Beta label

[jeff-schnitter]

Summary

• Adds cortex login command — prompts for workspace name and base URL, opens browser to the Cortex personal access tokens page (prefilled with workspace), validates the API key, and saves credentials to ~/.cortex/config
• Alphabetizes all commands in cortex --help output (including login and version in their correct positions)
• Removes "(Beta)" label from the workflows command — it is GA

Test plan

• cortex login with default workspace — browser opens, key validates, config written
• cortex login with custom workspace name — -t <workspace> shown in final message
• cortex login --no-open-browser — prints URL instead of opening browser
• cortex login --force — overwrites existing config without prompting
• cortex -h — all commands appear in alphabetical order
• cortex workflows --help — no Beta label

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