feat: add recurring transactions (Wiederkehrende Buchungen)

Lets treasurers/captains/coaches define recurring fee/levy dues that
are automatically booked for all active players on a monthly,
quarterly, or yearly schedule via a daily cron job, instead of having
to book them manually every cycle.

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

myteamwallet_backend/src/recurring-transactions/dto/create-recurring-transaction.dto.ts

@@ -0,0 +1,49 @@
+import { ApiProperty } from '@nestjs/swagger';
+import { Transform } from 'class-transformer';
+import {
+  IsIn,
+  IsInt,
+  IsNotEmpty,
+  IsNumber,
+  IsString,
+  Length,
+  Max,
+  Min,
+} from 'class-validator';
+import { TransactionTypeEnum } from 'src/transactions/transaction-type.enum';
+import { RecurringTransactionIntervalEnum } from '../recurring-transaction-interval.enum';
+
+const ALLOWED_TYPES = [TransactionTypeEnum.fee, TransactionTypeEnum.levy];
+
+export class CreateRecurringTransactionDTO {
+  @ApiProperty({ example: 2342 })
+  @IsInt()
+  @Min(1)
+  teamId: number;
+
+  @ApiProperty({ example: 'Monatsbeitrag' })
+  @Transform(({ value }) =>
+    typeof value === 'string' ? value.trim() : value,
+  )
+  @IsString()
+  @Length(1, 120)
+  description: string;
+
+  @ApiProperty({ example: 10 })
+  @IsNumber({ maxDecimalPlaces: 2 })
+  @Min(0.01)
+  @Max(10000)
+  amount: number;
+
+  @ApiProperty({ enum: ALLOWED_TYPES })
+  @IsIn(ALLOWED_TYPES)
+  type: TransactionTypeEnum;
+
+  @ApiProperty({ enum: RecurringTransactionIntervalEnum })
+  @IsIn(Object.values(RecurringTransactionIntervalEnum))
+  interval: RecurringTransactionIntervalEnum;
+
+  @ApiProperty({ example: 'isotimestring' })
+  @IsNotEmpty()
+  startDate: string;
+}