fix(ui): label combobox icon controls

[liljamesjohn]

Summary

• add accessible names to the default combobox popup trigger and clear button
• derive item-specific chip removal labels from string content, with a generic fallback
• allow consumers to customize trigger, clear, and chip removal labels

Fixes #11589.

Testing

• mise exec bun@latest -- pnpm registry:build
• mise exec bun@latest -- pnpm check
• NEXT_PUBLIC_APP_URL=http://localhost:4000 NEXT_PUBLIC_V0_URL=https://v0.dev mise exec bun@latest -- pnpm test (1,815 passed; one unrelated transformer test exceeded its 8-second timeout under parallel load and passed standalone)
• verified Base and Radix examples in browser accessibility trees: Open popup, Clear selection, and item-specific removal names are exposed

[vercel]

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