docs: Document spice cloud login subcommands

[claudespice]

Summary

• Document the restructured spice cloud login command with its three authentication methods: subscription (browser-based), pat (personal access token), and api (OAuth2 client credentials)

Source PRs

• Support OAuth2 client credentials in 'spice cloud login' spiceai#10586 — Support OAuth2 client credentials in 'spice cloud login'

Changes

• website/docs/cli/reference/login.md — Added spice cloud login section with documentation for subscription, pat, and api subcommands, including flags, environment variables, and usage examples

Test plan

• Verified subcommand names and flags match source code
• Verified environment variable names match source code
• Links are valid
• Version references are correct (vNext only — new feature)

[github-actions]

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[github-actions]

🚀 deployed to https://2de7003b.spiceai-org-website.pages.dev