Remove Palantir stacktrace dependency and use standard Go error handling

[wboayue]

Summary

• Replaced Palantir stacktrace with standard Go error wrapping using fmt.Errorf with %w verb
• Updated dependencies (removed unused Palantir dependency, updated test dependencies)
• Added CLAUDE.md documentation file for AI assistant guidance

Changes

• Error handling refactor: Migrated all error handling in client.go and transport.go from stacktrace.Propagate/NewError to idiomatic Go 1.13+ error wrapping
• Dependency cleanup: Removed github.com/palantir/stacktrace dependency and updated stretchr/testify to v1.11.0
• Documentation: Added comprehensive CLAUDE.md file with project overview, architecture, and development guidelines