fix(cli): use Phosphor SSR imports for RSC

[cyphercodes]

Summary

• Use Phosphor's SSR entrypoint when icon placeholders are transformed in React Server Component files.
• Preserve the regular Phosphor client entrypoint for files with "use client".

Fixes #10503

Test plan

• pnpm --filter=shadcn test -- src/utils/transformers/transform-icons.test.ts
• pnpm --filter=shadcn typecheck
• NODE_OPTIONS=--max-old-space-size=4096 pnpm --filter=shadcn build
• pnpm --filter=shadcn format:check
• pnpm exec prettier --check .changeset/calm-icons-serve.md packages/shadcn/src/icons/libraries.ts packages/shadcn/src/utils/transformers/transform-icons.ts packages/shadcn/src/utils/transformers/transform-icons.test.ts
• git diff --check

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