docs: document cloud status diagnostics

[KeuqS]

Summary

• Document sotto cloud status and sotto cloud status --json in the README.
• Explain the JSON response shape, older-server null results, billing URL behaviour, and the distinction from local sotto status.
• Keep the translated README files structurally aligned.

Verification

• Compared the documentation with the current CLI help and response types in crates/cli/src/main.rs and crates/cli/src/remote/api.rs.
• Verified the README translation structure, code blocks, links, inline code, headings, tables, and warning markers remain aligned.
• Documentation-only change; no runtime code or tests are affected.

Checklist

• This PR does not modify runtime behaviour or interfaces.
• The commit includes a DCO Signed-off-by line.

Closes #561

[github-actions]

Thanks for your first pull request to Sotto, and welcome.

Two things that trip up newcomers:

• Every commit needs a Signed-off-by line under the Developer Certificate of Origin - PRs with unsigned commits cannot be merged. Sign off with git commit -s; if your branch already has unsigned commits, run git rebase --signoff main and push again.
• Please run cargo fmt --all --check and cargo clippy --workspace --all-targets -- -D warnings before pushing, and add tests for new behaviour (cargo test --workspace runs the suite).

The full guide is in CONTRIBUTING.md - a maintainer will review shortly.

[Maxerns]

Verified in isolation:

• readme-i18n: all four translations in sync
• diff check: clean
• commit: signed off

I also checked the documented JSON shape field-by-field against EligibilityView, ServerInfo, and the cloud_status serialization.

That includes:

• the optional epoch fields
• the billing_available gate on billing_url
• the null behaviour for older servers
• login working without unlock
• the human-readable output claims

The example is clearly marked as synthetic, and the actions and dates are correctly described as values coming from the returned state rather than locally invented data.