fix(frontend): polish remaining zh-CN localization

[icatw]

Summary

• Localizes remaining Settings auth/resync, Session Vital Signs, vitals call rows, and sidebar multi-select UI copy through Paraglide.
• Converts remaining count-sensitive labels on status/sidebar/activity/insights/trash surfaces to plural-aware messages with separate formatted display labels.
• Refines zh-CN Session Vital Signs terminology and keeps agent names, tool names, file paths, commands, and session content unchanged.

Screenshots

zh-CN Session Vital Signs:

zh-CN Settings resync area:

zh-CN sidebar multi-select toolbar:

zh-CN Activity empty slot:

English switchback smoke:

[roborev-ci]

roborev: Combined Review (31c9716)

No Medium, High, or Critical findings to report.

The only reported issue was Low severity and has been omitted per the review-combination rules.

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Panel: ci_default_security | Synthesis: codex, 5s | Members: codex_default (codex/default, done, 2m45s), codex_security (codex/security, done, 13s) | Total: 3m3s

[roborev-ci]

roborev: Combined Review (393c18d)

Clean overall for security; one functional issue was reported, but it is below the requested severity threshold, so no Medium/High/Critical findings to include.

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Panel: ci_default_security | Synthesis: codex, 5s | Members: codex_default (codex/default, done, 3m3s), codex_security (codex/security, done, 32s) | Total: 3m40s