Move invoice PDF template from app/templates/invoices/ to
app/modules/orders/templates/invoices/ where InvoicePDFService expects it.
Expand invoice PDF tests to validate template path and existence.
Add unit tests for get_merchant_metrics() in tenancy, billing, and
customer metrics providers. Add unit tests for StatsAggregatorService
merchant methods. Add integration tests for the merchant dashboard
stats endpoint.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>