Add offline installation support with repo folder and updated dependencies

Features:
- Create repo/ folder structure for offline packages
  - python-wheels/ for Python packages (.whl files)
  - system-packages/ for APT packages and .deb files
- Add download_offline_packages.sh to populate Python wheels
- Add download_deb_packages.sh to download system .deb packages
- Update install.sh with smart online/offline detection
  - Auto-detects repo folder and uses offline packages
  - Falls back to online installation if repo is empty
  - Supports --offline flag for explicit offline mode
- Update requirements.txt with async dependencies:
  - aiohttp==3.9.1 for async HTTP client
  - asyncio==3.4.3 for async I/O framework
- Add OFFLINE_INSTALLATION.md with complete guide
- Add .gitignore to exclude downloaded packages from repo
- Document all system dependencies in apt-packages.txt

Downloaded packages:
- 18 Python wheels with all dependencies
- Total size: ~50 MB for Python packages
- Ready for offline deployment

requirements.txt

@@ -1,3 +1,5 @@
 kivy==2.1.0
 requests==2.32.4
-bcrypt==4.2.1
+bcrypt==4.2.1
+aiohttp==3.9.1
+asyncio==3.4.3