feat: link deposits to bill payment

apps/server/src/bills/dto/bill.dto.ts

@@ -1,16 +1,22 @@
-import { ArrayNotEmpty, IsArray, IsIn, IsInt, IsString } from 'class-validator';
+import { ArrayNotEmpty, IsArray, IsIn, IsInt, IsOptional, IsString, Matches } from 'class-validator';
 
 export class GenerateBillsDto {
   @IsString()
-  periodStart: string; // YYYY-MM-DD
+  @Matches(/^\d{4}-\d{2}$/)
+  billingMonth: string; // YYYY-MM
 
+  @IsOptional()
   @IsString()
-  periodEnd: string; // YYYY-MM-DD
+  periodStart?: string; // deprecated, derived from billingMonth
+
+  @IsOptional()
+  @IsString()
+  periodEnd?: string; // deprecated, derived from billingMonth
 }
 
 export class UpdateBillStatusDto {
-  @IsIn(['draft', 'confirmed', 'paid'])
-  status: 'draft' | 'confirmed' | 'paid';
+  @IsIn(['paid'])
+  status: 'paid';
 }
 
 export class BatchUpdateBillStatusDto extends UpdateBillStatusDto {