fix: refine AI Agent sidebar navigation

[huacnlee]

Summary

• move AI Agent directly after Account in all three locales
• keep AI Agent expanded while collapsing Workspace and Conversation so only the first level is visible
• replace the AI Agent CPU icon with a bot icon and add icons for Market and Screener
• preserve the configured expanded/collapsed state of all other sidebar sections

Test Plan

• generated the English, Simplified Chinese, and Traditional Chinese sidebars and asserted ordering, nesting, collapse state, and icon output
• ran Prettier checks on the changed sidebar/config files
• ran git diff --check
• build not run per repository instructions