fix(webui): Model Selection Optimization

[bobleer]

Summary

• Optimize the chat model selector so the trigger and tooltips show clearer resolved model names and concise provider/context metadata.
• Improve AI model configuration UX by rendering a compact multi-select value, disabling accidental mouse-wheel changes on numeric inputs, and refining related visual styles.
• Clarify the Chinese copy for custom model name entry in onboarding and settings.

Test plan

• pnpm run build:web

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