feat: Add Japanese and Korean localization

[alvis-HaoH]

Summary

• add Japanese (ja) and Korean (ko) localization support alongside the existing English, Chinese, and Turkish options
• detect Japanese and Korean system locales when the app language is set to follow the system
• extend localization tests to cover key completeness, representative strings, and placeholder formatting for both new languages

Why

The app already had a lightweight in-file localization path for Turkish. This extends the same mechanism so Japanese and Korean users can select those languages manually or have them picked up automatically from system locale settings.

User Impact

Users can now choose 日本語 or 한국어 in Settings, and system language mode will resolve to ja or ko when the system preferred language matches.

Validation

• swift test --filter L10nTests

[wxtsky]

翻译质量不错，测试覆盖也很全面 👍

提几个需要注意的点：

1. 与其他 PR 的 L10n key 冲突

以下已合并或待合并的 PR 新增了 L10n key，合并后需要补上日韩翻译：

• feat: add dismiss flow for permission prompts #93 (已 request changes): 新增 dismiss
• feature: add configurable auto-collapse after session jump #86 (已合并): 新增 auto_collapse_after_session_jump、auto_collapse_after_session_jump_desc
• feat: enhance message input with system tag parsing and double-click navigation #76 (待合并): 新增 send_message_placeholder、send_to_terminal、approval_input_placeholder、session_click_action、session_click_action_desc、click_action_terminal、click_action_message_input、remote_input_unsupported

建议 rebase 到最新 main 后，用你已有的 L10nTests 跑一下，缺失的 key 会自动报出来。

2. about_desc2 工具数量硬编码

日韩翻译里写的是 "8 種 CLI/IDE"，但目前支持的工具已经是 10 个了（刚合了 Kimi CLI）。请更新为实际数量。

3. 准备好后随时标记 Ready for Review

核心翻译部分没有问题，解决上面的冲突后可以直接出 Draft。