feat(billing): issue credit/debit memos against registered invoices

POST billing/invoices/:id/memo files a MoR DEB/CRE memo by reusing
createInvoice unchanged. sourceId is the original invoice's own id, not its
source's — this structurally keeps memos out of findPayable/expirePayable/
billQuery's sourceId-keyed lookups regardless of status. Credit notes are
created settled; debit notes are created open/unpaid as a genuine new
receivable, not force-settled. memoIssue is granted to the chief position,
not the general finance role.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/edr-freight-api/src/modules/billing/dto/issue-memo.dto.ts

@@ -0,0 +1,71 @@
+import { ApiProperty, ApiPropertyOptional } from "@nestjs/swagger";
+import { Type } from "class-transformer";
+import {
+  IsArray,
+  IsIn,
+  IsNumber,
+  IsObject,
+  IsOptional,
+  IsString,
+  Length,
+  ValidateNested,
+} from "class-validator";
+
+/** One line on a memo; omit the whole `lines` array on the parent DTO to copy the original's. */
+export class MemoLineDto {
+  @ApiProperty()
+  @IsString()
+  chargeType!: string;
+
+  @ApiPropertyOptional()
+  @IsOptional()
+  @IsString()
+  description?: string;
+
+  @ApiPropertyOptional()
+  @IsOptional()
+  @IsNumber()
+  quantity?: number;
+
+  @ApiPropertyOptional()
+  @IsOptional()
+  @IsNumber()
+  unitRate?: number;
+
+  @ApiPropertyOptional()
+  @IsOptional()
+  @IsNumber()
+  amount?: number;
+
+  @ApiPropertyOptional()
+  @IsOptional()
+  @IsString()
+  currency?: string;
+
+  @ApiPropertyOptional()
+  @IsOptional()
+  @IsObject()
+  metadata?: Record<string, unknown>;
+}
+
+/** `POST billing/invoices/:id/memo` body — see `BillingService.issueMemo`. */
+export class IssueMemoDto {
+  @ApiProperty({ enum: ["CRE", "DEB"], description: "MoR DocumentDetails.Type for the memo." })
+  @IsIn(["CRE", "DEB"])
+  type!: "CRE" | "DEB";
+
+  @ApiProperty({ description: "Why the memo was issued — MoR DocumentDetails.Reason." })
+  @IsString()
+  @Length(1, 500)
+  reason!: string;
+
+  @ApiPropertyOptional({
+    type: [MemoLineDto],
+    description: "Omit to copy every line of the original invoice verbatim.",
+  })
+  @IsOptional()
+  @IsArray()
+  @ValidateNested({ each: true })
+  @Type(() => MemoLineDto)
+  lines?: MemoLineDto[];
+}