Fix tsconfig path resolution for relative targets

[seveibar]

Summary

• ensure tsconfig path resolution joins path targets with the configured baseUrl
• cover baseUrl plus relative target scenario with a regression test
• replace Node path module usage with an internal join utility for browser compatibility

Testing

• bun test tests/features/tsconfig-paths-resolution.test.tsx
• bunx tsc --noEmit
• bun run format

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https://chatgpt.com/codex/tasks/task_b_68f000b231ec832eaea5547376adb060

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