test(core): cover directory barrel reachability (#1703)

* test: add comprehensive tests for barrel file directory imports

- Add tests for tsconfig path alias resolution to index.ts
- Add tests for baseUrl resolution to index.ts
- Add tests for relative directory imports to index.ts
- Add Next.js-specific test with auto-detected entries
- Add direct resolver tests to verify directory resolution

Tests confirm that barrel files imported via directory paths (e.g., @/features/foo -> foo/index.ts) are correctly resolved and not flagged as unused.

Related to issue #1699

Co-authored-by: Skosh <skoshx@users.noreply.github.com>

* test: add moduleResolution bundler test for directory imports

Test confirms that directory imports work correctly with moduleResolution: bundler setting (used by Next.js).

Co-authored-by: Skosh <skoshx@users.noreply.github.com>

* test(core): cover directory barrel reachability

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Skosh <skoshx@users.noreply.github.com>
Co-authored-by: Aiden Bai <aiden@million.dev>