Database
Declare a unique prefix such as hd_demo_. List owned tables/columns for migration and provide idempotent SQLite and MySQL statements for every migration ID. Statements may create/alter only plugin-owned tables.
Currency
Declare amountColumns, optional currencyColumn, safe where and precision (minor or decimal) so HotelDesk can convert eligible open values.
Web
Set web.enabled and include web/Plugin.php when web behavior is supported. Desktop installs/synchronizes the ZIP, status and configuration to the connected module. The web module never exposes plugin purchase/install/activation management.