New backend endpoint POST /invoices/{id}/convert-to-estimate that
creates a draft estimate from an invoice, copying items, taxes,
custom fields, and financial data. Frontend wired with dropdown
action, store method, and API service call.
V1/Admin -> Company (company-scoped controllers)
V1/SuperAdmin -> Admin (platform-wide admin controllers)
V1/Customer -> CustomerPortal (customer-facing portal)
V1/Installation -> Setup (installation wizard)
V1/PDF -> Pdf (consistent casing)
V1/Modules -> Modules (drop V1 prefix)
V1/Webhook -> Webhook (drop V1 prefix)
The V1 prefix served no purpose - API versioning is in the route prefix
(/api/v1/), not the controller namespace. "Admin" was misleading for
company-scoped controllers. "SuperAdmin" is now simply "Admin" for
platform administration.
