fix(cli): respect custom registry styles

[cyphercodes]

Summary

• Preserve custom configured styles in Tailwind v4 projects instead of always forcing new-york-v4.
• Keep the Tailwind v4 upgrade for legacy shadcn styles (default and new-york).
• Add regression coverage for custom registry styles and a patch changeset.

Fixes #10496

Verification

• pnpm --filter=shadcn test -- test/utils/get-config.test.ts
• pnpm --filter=shadcn typecheck
• pnpm --filter=shadcn format:check
• NODE_OPTIONS=--max-old-space-size=4096 pnpm --filter=shadcn build

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