docs: localize TUI images and refine terminal icons

[EF1874]

Summary

• reuse the existing docs/assets/tui.png for the TUI overview in both Chinese and English guides
• store only the Slash command menu screenshot as docs/assets/tui-slash-command-menu.png and reference it locally
• use SquareTerminal for the terminal group/folder and PanelsTopLeft for the TUI guide
• keep the CLI guides and their Terminal icon unchanged

Verification

• confirmed the branch is one commit directly on the latest upstream/main
• parsed all changed meta.json files
• verified all four local image references resolve and both referenced PNG signatures are valid
• confirmed the existing tui.png and both CLI guides are unchanged
• confirmed no Alidocs image URLs remain in the TUI guides
• ran git diff --check

[ZongYue99]

图片重复了，assets/下有个tui.png这个图片，咱们尽量复用哈，下次可以给我开个编辑权限，这样就不用麻烦你再改了哈～