Documentation: Remove hard-coded absolute paths from XCODE_SCHEME_SETUP.md

[leogdion]

Problem

Examples/Bushel/XCODE_SCHEME_SETUP.md contains hard-coded absolute paths that won't work for other developers.

Proposed Solution

Replace absolute paths with:

1. Relative paths from project root
2. Setup instructions for users to configure their own paths
3. Environment variable placeholders

Before:

/Users/specificuser/Documents/Projects/MistKit/Examples/Bushel

After:

$PROJECT_ROOT/Examples/Bushel

Or use relative paths:

Examples/Bushel

Impact

• Usability: Documentation works for all developers
• Onboarding: No confusion about paths
• Maintenance: Paths don't break when moved

Files Affected

• Examples/Bushel/XCODE_SCHEME_SETUP.md

References

• PR update from writing blog post and examples MistKit#129 CodeRabbit Review: update from writing blog post and examples MistKit#129 (XCODE_SCHEME_SETUP.md)
• Related: Add comprehensive test suite for Bushel demo MistKit#136, Add architecture diagrams to Bushel documentation MistKit#140