feat(flyer): add flyer session and selection system

- Add FlyerSession, FlyerItem, and FlyerSelection models to Prisma schema
- Implement session persistence with weekly key generation in FlyerImportService
- Add FlyerSelectionModule to AppModule
- Extend FlyerImportResponse with sessionId and flyerItemId fields
- Create new flyer-selection module directory structure
- Add migration for flyer session and selection tables

BREAKING CHANGE: Flyer import now persists data to FlyerSession and FlyerItem tables

backend/src/flyer-selection/dto/create-flyer-selection.dto.ts

@@ -0,0 +1,38 @@
+import { Type } from 'class-transformer';
+import {
+  IsIn,
+  IsInt,
+  IsNumber,
+  IsOptional,
+  IsString,
+  MaxLength,
+  Min,
+} from 'class-validator';
+
+export class CreateFlyerSelectionDto {
+  @Type(() => Number)
+  @IsInt()
+  @Min(1)
+  itemId!: number;
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsNumber({ maxDecimalPlaces: 2 })
+  @Min(0)
+  plannedQuantity?: number;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(24)
+  plannedUnit?: string;
+
+  @IsOptional()
+  @IsString()
+  @IsIn(['low', 'normal', 'high'])
+  priority?: string;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(500)
+  note?: string;
+}

backend/src/flyer-selection/dto/flyer-selection.response.ts

@@ -0,0 +1,22 @@
+export type FlyerSelectionResponse = {
+  id: number;
+  sessionId: number;
+  itemId: number;
+  userId: number;
+  plannedQuantity: number | null;
+  plannedUnit: string | null;
+  priority: string;
+  note: string | null;
+  status: string;
+  createdAt: string;
+  updatedAt: string;
+  item: {
+    id: number;
+    rawName: string;
+    normalizedName: string;
+    price: number | null;
+    priceUnit: string | null;
+    matchedProductId: number | null;
+    matchedProductName: string | null;
+  };
+};

backend/src/flyer-selection/dto/update-flyer-selection.dto.ts

@@ -0,0 +1,37 @@
+import { Type } from 'class-transformer';
+import {
+  IsIn,
+  IsNumber,
+  IsOptional,
+  IsString,
+  MaxLength,
+  Min,
+} from 'class-validator';
+
+export class UpdateFlyerSelectionDto {
+  @IsOptional()
+  @Type(() => Number)
+  @IsNumber({ maxDecimalPlaces: 2 })
+  @Min(0)
+  plannedQuantity?: number;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(24)
+  plannedUnit?: string;
+
+  @IsOptional()
+  @IsString()
+  @IsIn(['low', 'normal', 'high'])
+  priority?: string;
+
+  @IsOptional()
+  @IsString()
+  @IsIn(['planned', 'bought', 'skipped', 'archived'])
+  status?: string;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(500)
+  note?: string;
+}