Add zh-CN localization for embedded dashboard

[vimalinx]

Summary

• add a lightweight runtime i18n layer (zh-CN + en) for the embedded dashboard UI
• localize common shell text, toasts, confirm dialogs, status/error strings, and markdown copy button labels
• add a locale toggle in the header and wire locale-aware date/number formatting in scheduler and hands pages
• include related lint-safe JS refactors and a small clippy cleanup in CLI diagnostics path

Verification

• cargo build --workspace --lib
• cargo test --workspace
• cargo clippy --workspace --all-targets -- -D warnings

[Jengro777]

@vimalinx
Is there any new progress?

[jaberjaber23]

Reviewed and approved. Has merge conflicts with recent changes. Please rebase onto current main and we will merge.

[Jengro777]

@vimalinx
Looking forward to