Returns every project ID owned by the given merchant. Read-only, runs via Soroban simulation and does not consume fees.
Parameters
Return value
Vec<u64> — the project IDs. Order is insertion order on chain.
An empty vec means the merchant has not created any projects yet.
Examples
Pair this with get_merchant_plans and the plan’s project_id field to
reconstruct the full “project → plans” tree a merchant has on chain.