refactor(label): standardize label keys

[hellomypastor]

Summary

• Updated sandbox label namespaces from sandbox.dev to opensandbox.io and normalized label suffixes to kebab-case (expires-at, embedding-proxy-port, http-port, id) across services, tests, and docs to
  match the new domain/label conventions.
• Swapped all remaining opensandbox.dev references (including wildcard domains) to opensandbox.io and updated SDK documentation domains from api.opensandbox.dev to api.opensandbox.io for consistency.

Testing

• Not run (explain why)
• Unit tests
• Integration tests
• e2e / manual verification

Breaking Changes

• None
• Yes (describe impact and migration path)
  • Docker labels now use the opensandbox.io prefix and kebab-case keys; existing containers/scripts/tests expecting sandbox.dev/* or camelCase label names must update to the new keys.

Checklist

• Linked Issue or clearly described motivation
• Added/updated docs (if needed)
• Added/updated tests (if needed)
• Security impact considered
• Backward compatibility considered

[Pangjiping]

LGTM