* feat(web): show disabled reasons in tooltips when buttons are disabled
- Add disabled reason tooltips for model card actions (set default, delete)
- Add disabled reason tooltips for marketplace skill card install button
- Add disabled reason display for chat input when disabled
- Add internationalization support for all disabled reasons (en/zh)
- Model card: Show specific reasons when set-default or delete buttons are disabled
- Marketplace skill card: Show specific reasons when install button is disabled
- Chat composer: Show reason text below input when input is disabled
* fix: show disabled action reasons via tooltips
* fix(web): restore accessible labels for model action tooltips
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