fix: support asChild in SelectTrigger

[raashish1601]

Summary

• Avoid rendering the built-in select chevron as a sibling when SelectTrigger is used with asChild.
• Preserve the default chevron icon for the normal trigger path.
• Regenerate the v4 Radix style outputs and public registry JSON.
• Add regression coverage for the single-child asChild contract.

Fixes #8075.

Tests

• corepack pnpm exec vitest run apps/v4/registry/select-trigger.test.tsx
• corepack pnpm --filter=v4 lint
• corepack pnpm --filter=v4 typecheck
• corepack pnpm --filter=shadcn build
• corepack pnpm dlx bun run ./scripts/build-registry.mts from apps/v4
• corepack pnpm exec prettier --check <changed files>
• git diff --check

[vercel]

@raashish1601 is attempting to deploy a commit to the shadcn-pro Team on Vercel.

A member of the Team first needs to authorize it.