refactor: Reorganize documentation and fix requirements.txt

[thebtf]

Documentation Changes:

• Move all documentation to docs/ directory for better organization
• Keep only README.md and CLAUDE.md in root
• Create docs/README.md with comprehensive documentation index
• Update all internal links to point to docs/ directory

Files moved to docs/:

• CHANGELOG.md
• BUILD.md
• MANUAL_BUILD.md
• ARCHITECTURES.md
• DOCKER.md
• CONTRIBUTING.md
• RELEASE_v1.4.0.md
• CREATE_PR_STEPS.md
• PR_DESCRIPTION.md

Requirements.txt fix:

• Replace exact versions with flexible version ranges
• Use >= and < constraints for compatibility
• Allows pip to find compatible versions in PyPI
• Fixes Docker build error: 'pip install failed with exit code 1'

Benefits:

• Cleaner repository structure
• Easier to navigate documentation
• Better separation of concerns
• Resolves package installation issues