Creates a Project on chain. A Project groups billing plans together under a single merchant: one merchant can own many projects, and each plan is scoped to exactly one. Returns the chain-assigned project_id (a globally unique u64).
Every plan must reference an existing project, so merchants must create a Project before they can create any plans.
Parameters
Authorization
The merchant address must sign.
Return value
u64 — the new project_id.
Events emitted
Examples
Projects are cheap to create and can’t be deleted, so you typically
create one per product line. Each plan belongs to exactly one project.