feat: add jp translation

Adds the Japanese translation file app_jp.arb to the lib/l10n directory, expanding the app's internationalization support.

Translation Coverage: Includes comprehensive translations for UI elements, error messages, settings, and user interactions, ensuring a localized experience for Japanese users.
User Interaction: Translates system messages, chat commands, and prompts, facilitating smoother engagement for Japanese-speaking audiences.
Settings and Features: Localizes settings, features descriptions, and warnings, such as audio source permissions and stream preview notices, enhancing usability for the target demographic.

For more details, open the Copilot Workspace session.

muxable / rtchat