[D1] Customer entity (name/phone/address) + CRUD #10

Sprint D · Sales · area:domain area:api

SalesOrder.CustomerId is referenced but there is no Customer entity. MVP customer stays close to the reference app (Order: name, phone, address), plus email.

Fields (MVP)

• name — required
• phone — required
• email — optional
• address — optional (delivery)
• note — optional (free text)

Out of scope (→ Phase 1.1): balances/credit terms, tax id, payments.

Scope

• Customer aggregate with the fields above + account/tenant id.
• CRUD endpoints: create, list, get.

Done when: a customer can be created and referenced by a sales order.

Migrated from Gitea issue #10 (https://gitea.mforcelabs.com/mforce/cluckwork/issues/10).