fix(cloud): remove viewer organization role

[VantaNode]

Summary

• remove Viewer from Cloud organization invite and member role selectors
• centralize the supported roster roles as owner/admin/member and assignable roles as admin/member
• reject removed Viewer values at the org roster, member roster, and invite response wire boundaries
• remove the obsolete Viewer copy from all 13 navigation locales while retaining unrelated live-presence viewer semantics

Testing

• npm run typecheck
• npm run lint
• npm test -- --run (444 files, 5129 tests)
• npm run check:i18n:cloud
• targeted Org2Cloud tests (4 files, 75 tests)
• node --check tests/e2e/specs/core/cloud-dual-instance-ui.spec.mjs
• git diff --check

E2E coverage

The real dual-instance Cloud scenario now opens both role selectors and asserts that Viewer is absent before exercising the supported member-to-admin promotion flow. It was not executed locally because this checkout has no tests/e2e/.env Cloud credentials; the spec syntax and all local gates above pass.