feat(zh-CN): add 75 missing Chinese translations across 6 files

[BeoKa-cita]

Summary

Completes the zh-CN localization by translating 75 previously missing strings across 6 JSON files.

Files changed:

• zh-CN/chat.json - Clear last used model action, speculative decoding UI, MCP plugin auth
• zh-CN/config.json - Parallel sessions, KV cache, chat template, MoE CPU offload, preset saving
• zh-CN/developer.json - API endpoint labels (Anthropic/OpenAI compat), MCP permission, server control
• zh-CN/models.json - Memory guardrails, GPU selection, model variant switching
• zh-CN/settings.json - Nav bar position, default context length, JIT TTL, model defaults
• zh-CN/shared.json - Beta label

Translation approach

• Consistent with existing zh-CN terminology and style
• Preserved all template placeholders ({{variable}}, <altOptionKey />)
• Used simplified Chinese (Mainland China) throughout

Closes: N/A - community translation completion

[github-actions]

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