docs: update README and implementation plan with Phase 0-4 completion status

[loki-hermes-agent]

Summary

Updates the project documentation to reflect the successful completion of Phases 0 through 4.

Changes:

• Updated README.md project structure to include all newly created modules (context.py, baselines.py, approval.py, executor.py) and their corresponding test files.
• Updated test suite statistics to reflect the current state (161 tests passing, 90% coverage).
• Updated the Phase Status table in README.md to mark Phases 2, 3, and 4 as ✅ Complete.
• Updated docs/hermes-implementation-plan.md to mark Task 15 as complete.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation