fix(shadcn): preserve binary registry files

[hugosmoreira]

Summary

• encode binary registry file contents as base64 during shadcn build
• decode base64 payloads back to their original bytes during installation
• compare existing binary files byte-for-byte and exclude them from source transforms
• expose the optional encoding: "base64" field in the registry item schemas
• add a patch changeset and focused build/install regressions

Root cause

The registry builder read every source file as UTF-8. Binary bytes that are not valid UTF-8 were replaced before the content was serialized to JSON, and the installer later wrote that damaged string back to disk as UTF-8.

Text registry files keep their existing representation. Only content containing null bytes or failing a lossless UTF-8 round trip is base64-encoded.

Validation

• vitest run packages/shadcn/src/commands/build.test.ts — 2 tests passed
• focused binary build/install regressions — 2 tests passed
• tsc --noEmit for packages/shadcn
• ESLint for all changed TypeScript files
• Prettier check for all changed files
• changeset status

Fixes #7287

[vercel]

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

A member of the Team first needs to authorize it.