Fix css-tailwind extra trailing newline

[Jalendar10]

Summary

Closes #139 by preventing css-tailwind exports from adding an extra newline at the CLI layer.

Changes

• Writes serialized Tailwind v4 CSS directly with process.stdout.write(...) instead of console.log(...).
• Adds an export command regression test that verifies css-tailwind output ends with exactly one newline.

Validation

• bun test packages/cli/src/commands/export.test.ts
• bun test packages/cli/src/commands packages/cli/src/linter/tailwind/v4
• bun run --cwd packages/cli lint
• bun run --cwd packages/cli build
• bun test
• Byte-level reproduction now reports one trailing newline byte:
  • b'primary: #ffffff;\n}\n'
  • 1

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