Update Claude API implementation plan with technical corrections

- Add missing anthropic-version header requirement for authentication
- Fix request/response models to match actual Claude API structure:
  * ContentBlock arrays instead of simple strings
  * System parameter support for Claude-specific system messages
  * Claude-specific tool calling format
  * Image content support via ContentBlock structure
- Update build configuration with Scala 3 priority and projectMatrix integration
- Refine testing strategy to focus on Claude-specific functionality
- Update implementation phases with Claude-specific technical details
- Add mandatory code formatting workflow documentation

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: lukaszlenart