feat: Add SQLite database integration for aircraft history and callsign enhancement

- Implement comprehensive database package with versioned migrations
- Add skyview-data CLI tool for managing aviation reference data
- Integrate database with merger for real-time aircraft history persistence
- Support OurAirports and OpenFlights data sources (runtime loading)
- Add systemd timer for automated database updates
- Fix transaction-based bulk loading for 2400% performance improvement
- Add callsign enhancement system with airline/airport lookups
- Update Debian packaging with database directory and permissions

Database features:
- Aircraft position history with configurable retention
- External aviation data loading (airlines, airports)
- Callsign parsing and enhancement
- API client for external lookups (OpenSky, etc.)
- Privacy mode for complete offline operation

CLI commands:
- skyview-data status: Show database statistics
- skyview-data update: Load aviation reference data
- skyview-data list: Show available data sources
- skyview-data clear: Remove specific data sources

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

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

debian/usr/share/doc/skyview-adsb/DATABASE.md

@@ -0,0 +1,99 @@
+# SkyView Database Management
+
+SkyView includes a comprehensive database management system for enriching aircraft callsigns with airline and airport information.
+
+## Quick Start
+
+### 1. Check Current Status
+```bash
+skyview-data status
+```
+
+### 2. Import Safe Data (Recommended)
+```bash
+# Import public domain sources automatically
+skyview-data update
+```
+
+### 3. Enable Automatic Updates (Optional)
+```bash
+# Weekly updates on Sunday at 3 AM
+sudo systemctl enable --now skyview-database-update.timer
+```
+
+## Available Data Sources
+
+### Safe Sources (Public Domain)
+These sources are imported automatically with `skyview-data update`:
+- **OurAirports**: Comprehensive airport database (public domain)
+- **FAA Registry**: US aircraft registration data (public domain)
+
+### License-Required Sources  
+These require explicit acceptance:
+- **OpenFlights**: Airline and airport data (AGPL-3.0 license)
+
+## Commands
+
+### Basic Operations
+```bash
+skyview-data list                    # Show available sources
+skyview-data status                  # Show database status  
+skyview-data update                  # Update safe sources
+skyview-data import openflights     # Import licensed source
+skyview-data clear <source>         # Remove source data
+```
+
+### Systemd Timer Management
+```bash
+# Enable weekly automatic updates
+systemctl enable skyview-database-update.timer
+systemctl start skyview-database-update.timer
+
+# Check timer status
+systemctl status skyview-database-update.timer
+
+# View update logs
+journalctl -u skyview-database-update.service
+
+# Disable automatic updates
+systemctl disable skyview-database-update.timer
+```
+
+## License Compliance
+
+SkyView maintains strict license separation:
+- **SkyView binary**: Contains no external data (stays MIT licensed)
+- **Runtime import**: Users choose which sources to import
+- **Safe defaults**: Only public domain sources updated automatically
+- **User choice**: Each person decides their own license compatibility
+
+## Troubleshooting
+
+### Check Service Status
+```bash
+systemctl status skyview-database-update.timer
+journalctl -u skyview-database-update.service -f
+```
+
+### Manual Database Reset
+```bash
+systemctl stop skyview-database-update.timer
+skyview-data reset --force
+skyview-data update
+systemctl start skyview-database-update.timer
+```
+
+### Permissions Issues
+```bash
+sudo chown skyview:skyview /var/lib/skyview/
+sudo chmod 755 /var/lib/skyview/
+```
+
+## Files and Directories
+
+- `/usr/bin/skyview-data` - Database management command
+- `/var/lib/skyview/skyview.db` - Database file  
+- `/usr/share/skyview/scripts/update-database.sh` - Cron helper script
+- `/lib/systemd/system/skyview-database-update.*` - Systemd timer files
+
+For detailed information, see `man skyview-data`.