Integrate parallel algorithm with existing system

[oleander]

Task

Integrate the new parallel implementation with the existing codebase infrastructure.

Requirements

• Modify primary entry point in src/commit.rs to use optimized parallel approach
• Maintain fallback to local generation or single-step approaches
• Update debug output infrastructure in src/debug_output.rs:
  • Track time spent in parallel analysis
  • Track time spent in synthesis
  • Track overall end-to-end processing time
• Respect all existing configuration settings:
  • User-specified model selection
  • Maximum message length
  • API timeout values
  • Other parameters affecting system behavior
• Maintain compatibility with existing error handling patterns
• Use standard Result type with anyhow context
• Ensure clear, actionable error messages

Success Criteria

• Seamless integration with existing codebase
• Performance improvements measurable via debug output
• Works correctly with default and customized settings
• Error messages are clear and guide users to resolution
• Authentication failures, network errors, and rate limiting clearly identified

Part of #81