feat: add firmware versioning and device_type support (NebuleAir/ModuleAir)

- Add VERSION file (1.0.0) and changelog.json for firmware tracking
- Add device_type config param (nebuleair_pro default, backward compatible via INSERT OR IGNORE)
- Add device_type select in admin.html Protected Settings
- Add version badge and changelog modal in Updates section
- Add get_firmware_version and get_changelog PHP endpoints
- Display firmware version in update_firmware.sh after git pull

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

update_firmware.sh

@@ -57,6 +57,11 @@ fi
 git pull origin $(git branch --show-current)
 check_status "Git pull"
 
+# Display firmware version
+if [ -f "/var/www/nebuleair_pro_4g/VERSION" ]; then
+    print_status "Firmware version: $(cat /var/www/nebuleair_pro_4g/VERSION)"
+fi
+
 # Step 2: Update database configuration
 print_status ""
 print_status "Step 2: Updating database configuration..."