fix: resolve absolute outDir paths correctly

[koistya]

Summary

• Fix path resolution when outDir is an absolute path by using resolve() instead of join()
• Display relative paths in CLI output for cleaner presentation
• Add test coverage for absolute outDir with custom root

Problem

When using an absolute outDir with a custom root, the join() function incorrectly concatenates paths:

// Before: join("/project", "/tmp/output") → "/project/tmp/output" ❌
// After: resolve("/project", "/tmp/output") → "/tmp/output" ✓

Test plan

• Added e2e test for absolute outDir with custom root
• Run bun test to verify all tests pass