feat(manifest): add externalNumber reference to quote/order/delivery

- Add `external_number NVARCHAR(100)` column to the `manifest` table.
- Thread `externalNumber` through manifestDoc and delivery SQL (list,
  header, create, update).
- Include `externalNumber` in shapeSummary and quote/order/delivery
  create/update/list/getById handlers (optional, clearable on update).
- Update README type definitions and regenerate API/schema docs.

src/schema.js

@@ -537,6 +537,7 @@ BEGIN
         [number] NVARCHAR(100) NOT NULL,
         [type] NVARCHAR(100) NOT NULL,
         entity_id INT NULL,
+        external_number NVARCHAR(100) NULL,
         [date] DATETIME2 NOT NULL CONSTRAINT DF_manifest_date DEFAULT SYSUTCDATETIME(),
         CONSTRAINT FK_manifest_company FOREIGN KEY (company_id) REFERENCES company(id) ON DELETE NO ACTION,
         CONSTRAINT FK_manifest_entity FOREIGN KEY (entity_id) REFERENCES entity(id) ON DELETE SET NULL