fix: Correct systemd configuration and Debian package setup

- Fix database update service to include config path parameter
- Move ConditionACPower from [Timer] to [Unit] section in timer config
- Add database directory to ReadWritePaths in main service
- Set explicit database path in Debian package config template
- Simplify postinst script to be quiet and use consistent skyview-adsb user
- Update README.Debian with comprehensive systemd service documentation
- Remove confusing dual-user setup in favor of single skyview-adsb user

SystemD Configuration Summary:
- Main service: skyview-adsb.service with database pre-update
- Database service: skyview-database-update.service (oneshot)
- Weekly timer: skyview-database-update.timer (Sunday 3AM with randomization)
- All services use skyview-adsb user consistently
- Database path: /var/lib/skyview-adsb/skyview.db
- Config path: /etc/skyview-adsb/config.json

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

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

debian/etc/skyview-adsb/config.json

@@ -0,0 +1,54 @@
+{
+  "server": {
+    "host": "",
+    "port": 8080
+  },
+  "sources": [
+    {
+      "id": "primary",
+      "name": "Primary Receiver",
+      "host": "localhost",
+      "port": 30005,
+      "latitude": 0.0,
+      "longitude": 0.0,
+      "altitude": 0.0,
+      "enabled": true
+    }
+  ],
+  "origin": {
+    "latitude": 0.0,
+    "longitude": 0.0,
+    "name": "Receiver Location"
+  },
+  "settings": {
+    "history_limit": 1000,
+    "stale_timeout": 60,
+    "update_rate": 1
+  },
+  "database": {
+    "path": "/var/lib/skyview-adsb/skyview.db",
+    "max_history_days": 7,
+    "backup_on_upgrade": true,
+    "max_open_conns": 10,
+    "max_idle_conns": 5
+  },
+  "callsign": {
+    "enabled": true,
+    "cache_hours": 24,
+    "privacy_mode": false,
+    "sources": {
+      "openflights_airlines": {
+        "enabled": true,
+        "priority": 1
+      },
+      "openflights_airports": {
+        "enabled": true,
+        "priority": 2
+      },
+      "ourairports": {
+        "enabled": true,
+        "priority": 3
+      }
+    }
+  }
+}