docs(FR-2325): add screenshots and improve RBAC Management documentation

Add language-specific screenshots (EN, KO, JA) for all 9 RBAC Management
UI states: role list, create/edit role modals, role detail drawer,
assignments tab, add/remove user dialogs, permissions tab, and add
permission modal. TH uses EN screenshots as placeholders since Thai
locale is not available in the current deployment.

Also applies reviewer feedback: fix terminology, version references,
cross-reference links, and field descriptions across all 4 languages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ironAiken2