docs: improve documentation and clean up AI-generated content

- Simplified README.md: removed marketing language, more natural tone
- Updated SECURITY.md: replaced placeholder with practical security policy
- Improved CONTRIBUTING.md: clearer instructions, concise formatting
- Cleaned requirements.txt: removed verbose comments
- Updated issue templates: Python-specific, learner-friendly
- Refined code comments in Basics directory:
  - 01_if_else.py: fixed unnatural spacing in strings
  - 01_class_basics.py: improved naming, added docstrings
  - 15_set_methods.py: simplified verbose comments
  - 16_dict_basics.py: cleaner formatting, practical comments
  - 08_file_search_log.py: natural language comments
- Enhanced rest_api/main.py: added docstrings, better comments
- Removed: .github/ISSUES_TO_CREATE/ (63 duplicate AI-generated issues)

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

Author: hackdartstorm