chore: update documentation for recent changes

[brennercruvinel]

Tasks

• Update README.md command count (24 not 25)
• Document validation phases in README
• Update CONTRIBUTING.md with new guidelines
• Ensure CHANGELOG reflects all changes

Changes Made

• Removed /human-mode command
• Added extended thinking capability
• Added validation phases
• Clean code standards (no emojis)

[brennercruvinel]

Implemented in PR #52