docs: add comprehensive README files across the codebase

Add 180+ new README files automatically generated across the codebase:
- Core modules: admin/, api/, cache/, decorators/, extensions/, forms/, middleware/, models/, utils/, validators/
- Django apps: accounts/, changelog/, organizations/, cpq/, and 25+ additional apps
- External integrations: lib/google/, lib/stripe/, lib/slack/, lib/aws/, lib/github/, and 40+ third-party library wrappers
- Utilities: scripts/, south_migrations/, templatetags/, test_scaffold/

These README files provide clear, concise module summaries for improved code navigation and documentation.

Updated existing README files for main project and key modules.

Corrected Hacktoolkit branding to proper capitalization (only H capitalized).

Updated .gitignore to exclude MkDocs build artifacts (site/).

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: YosefAshenafi