feat(shopping-list): add shopping list feature with flyer integration

This commit introduces a comprehensive shopping list feature with the following key changes:

Backend:
- Added ShoppingListItem model with relations to User, Product, and Category
- Added new fields to FlyerSession for source file metadata
- Added categoryId field to FlyerItem model
- Implemented session source file retrieval endpoint
- Added endpoint for updating flyer session items with category assignment
- Added endpoint for planning flyer selections to shopping list
- Implemented backfillCategoriesMine for AI-assisted category assignment
- Added ShoppingListModule and integrated with FlyerSelectionModule

Frontend:
- Added ShoppingListScreen and navigation route
- Implemented API paths and client methods for shopping list operations
- Added category tree loading for shopping list item creation
- Integrated shopping list functionality in flyer import tab
- Added category backfill trigger in inventory screen
- Updated FlyerImportItem model with categoryId support
- Added methods for updating flyer session items and retrieving source files

Database:
- Added new Prisma migration for flyer source metadata and shopping list items
- Updated schema with new relations and indexes

The shopping list feature allows users to:
1. Plan flyer selections directly to their shopping list
2. View and manage their shopping list items
3. Update flyer session items with proper categorization
4. Retrieve original flyer source files
5. Automatically backfill categories for uncategorized products

backend/prisma/schema.prisma

@@ -32,6 +32,7 @@ model User {
   unitMappings     UnitMapping[]
   flyerSessions    FlyerSession[]
   flyerSelections  FlyerSelection[]
+  shoppingListItems ShoppingListItem[]
 }
 
 model Product {
@@ -57,16 +58,19 @@ model Product {
   categoryId        Int?
   categoryRef       Category?       @relation(fields: [categoryId], references: [id], onDelete: SetNull)
   isPrivate         Boolean         @default(false)
-  unitMappings      UnitMapping[]
-}
+  unitMappings      UnitMapping[]
+  shoppingListItems ShoppingListItem[]
+}
 
 model Category {
   id       Int        @id @default(autoincrement())
   name     String
   parentId Int?
   parent   Category?  @relation("CategoryTree", fields: [parentId], references: [id], onDelete: SetNull)
-  children Category[] @relation("CategoryTree")
-  products Product[]
+  children Category[] @relation("CategoryTree")
+  products Product[]
+  flyerItems FlyerItem[]
+  shoppingListItems ShoppingListItem[]
 
   @@unique([name, parentId])
   @@index([parentId])
@@ -289,6 +293,11 @@ model FlyerSession {
   createdAt  DateTime         @default(now())
   updatedAt  DateTime         @updatedAt
   expiresAt  DateTime?
+  sourceFileName String?
+  sourceMimeType String?
+  sourceFileSize Int?
+  sourceStorageKey String?
+  sourceData  Bytes?
 
   user       User             @relation(fields: [userId], references: [id], onDelete: Cascade)
   items      FlyerItem[]
@@ -305,6 +314,7 @@ model FlyerItem {
   rawName            String
   normalizedName     String
   categoryHint       String?
+  categoryId         Int?
   price              Decimal?         @db.Decimal(10, 2)
   priceUnit          String?
   comparisonPrice    Decimal?         @db.Decimal(10, 2)
@@ -321,10 +331,12 @@ model FlyerItem {
   updatedAt          DateTime         @updatedAt
 
   session            FlyerSession     @relation(fields: [sessionId], references: [id], onDelete: Cascade)
+  categoryRef        Category?        @relation(fields: [categoryId], references: [id], onDelete: SetNull)
   selections         FlyerSelection[]
 
   @@index([sessionId])
   @@index([normalizedName])
+  @@index([categoryId])
 }
 
 model FlyerSelection {
@@ -348,3 +360,26 @@ model FlyerSelection {
   @@index([sessionId])
   @@index([userId, status])
 }
+
+model ShoppingListItem {
+  id         Int      @id @default(autoincrement())
+  userId     Int
+  name       String
+  productId  Int?
+  categoryId Int?
+  quantity   Decimal? @db.Decimal(10, 2)
+  unit       String?
+  source     String   @default("manual")
+  status     String   @default("open")
+  checkedAt  DateTime?
+  createdAt  DateTime @default(now())
+  updatedAt  DateTime @updatedAt
+
+  user       User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  product    Product? @relation(fields: [productId], references: [id], onDelete: SetNull)
+  categoryRef Category? @relation(fields: [categoryId], references: [id], onDelete: SetNull)
+
+  @@index([userId, status])
+  @@index([productId, unit, status])
+  @@index([categoryId])
+}