Add offline installation quick start guide

OFFLINE_QUICKSTART.md

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+# Offline Installation Quick Start
+
+## For Connected System (Preparation)
+
+```bash
+# 1. Download Python packages (required)
+bash download_offline_packages.sh
+
+# 2. Download system .deb packages (optional, for fully offline)
+bash download_deb_packages.sh
+```
+
+## For Offline System (Installation)
+
+```bash
+# The installer auto-detects offline packages
+bash install.sh
+
+# Or explicitly use offline mode
+bash install.sh --offline
+```
+
+## What's Included
+
+### Python Packages (18 wheels)
+✅ Kivy 2.1.0  
+✅ Requests 2.32.4  
+✅ Bcrypt 4.2.1  
+✅ Aiohttp 3.9.1 (async HTTP)  
+✅ Asyncio 3.4.3 (async framework)  
+✅ All dependencies
+
+### System Packages
+📋 See `repo/system-packages/apt-packages.txt`
+
+## File Size
+- Python wheels: ~50 MB
+- System packages: ~200-500 MB (if .deb downloaded)
+
+## See Also
+- **OFFLINE_INSTALLATION.md** - Complete guide
+- **repo/README.md** - Repository structure