Add Japanese translations for Agent Skills and Theming MCP topics

Agent-Logs-Url: https://github.com/IgniteUI/igniteui-xplat-docs/sessions/6e7e20ed-8247-4dac-8a2d-0f3fc40c9c2f

Co-authored-by: damyanpetev <3198469+damyanpetev@users.noreply.github.com>

Author: Copilot