feat: add updateCategoryMine endpoint to manage product category updates

- Implemented a new PATCH endpoint in ProductsController to update the category of a user's product.
- Added corresponding service method in ProductsService to handle business logic and validation.
- Created UpdateCategoryMineDto for request validation.
- Enhanced error handling for forbidden actions and not found resources.
- Updated API error mapping in Flutter to handle specific forbidden messages.
- Modified ProductPickerField to allow product creation directly from the picker.
- Added tests for the new endpoint and service method to ensure proper functionality and error handling.

backend/src/products/products.service.spec.ts

@@ -0,0 +1,91 @@
+import { ForbiddenException, NotFoundException } from '@nestjs/common';
+import { ProductsService } from './products.service';
+
+describe('ProductsService.updateCategoryMine', () => {
+  const prismaMock = {
+    product: {
+      findUnique: jest.fn(),
+      update: jest.fn(),
+    },
+    category: {
+      findUnique: jest.fn(),
+    },
+  };
+
+  const aiServiceMock = {
+    suggestCategory: jest.fn(),
+  };
+
+  const categoriesServiceMock = {
+    findFlattened: jest.fn(),
+  };
+
+  const service = new ProductsService(
+    prismaMock as any,
+    aiServiceMock as any,
+    categoriesServiceMock as any,
+  );
+
+  beforeEach(() => {
+    jest.clearAllMocks();
+  });
+
+  it('kastar NotFound om produkt saknas', async () => {
+    prismaMock.product.findUnique.mockResolvedValue(null);
+
+    await expect(service.updateCategoryMine(42, 100, 5)).rejects.toBeInstanceOf(NotFoundException);
+  });
+
+  it('kastar Forbidden om produkten inte ägs av användaren', async () => {
+    prismaMock.product.findUnique.mockResolvedValue({
+      id: 100,
+      ownerId: 7,
+      isPrivate: true,
+    });
+
+    await expect(service.updateCategoryMine(42, 100, 5)).rejects.toBeInstanceOf(ForbiddenException);
+  });
+
+  it('kastar Forbidden för globala produkter', async () => {
+    prismaMock.product.findUnique.mockResolvedValue({
+      id: 100,
+      ownerId: 42,
+      isPrivate: false,
+    });
+
+    await expect(service.updateCategoryMine(42, 100, 5)).rejects.toBeInstanceOf(ForbiddenException);
+    expect(prismaMock.product.update).not.toHaveBeenCalled();
+  });
+
+  it('kastar NotFound om kategori saknas', async () => {
+    prismaMock.product.findUnique.mockResolvedValue({
+      id: 100,
+      ownerId: 42,
+      isPrivate: true,
+    });
+    prismaMock.category.findUnique.mockResolvedValue(null);
+
+    await expect(service.updateCategoryMine(42, 100, 9999)).rejects.toBeInstanceOf(NotFoundException);
+    expect(prismaMock.product.update).not.toHaveBeenCalled();
+  });
+
+  it('uppdaterar kategori för ägd icke-global produkt', async () => {
+    prismaMock.product.findUnique.mockResolvedValue({
+      id: 100,
+      ownerId: 42,
+      isPrivate: true,
+    });
+    prismaMock.category.findUnique.mockResolvedValue({ id: 5 });
+    prismaMock.product.update.mockResolvedValue({ id: 100, categoryId: 5 });
+
+    await expect(service.updateCategoryMine(42, 100, 5)).resolves.toEqual({
+      id: 100,
+      categoryId: 5,
+    });
+    expect(prismaMock.product.update).toHaveBeenCalledWith({
+      where: { id: 100 },
+      data: { categoryId: 5 },
+      select: { id: true, categoryId: true },
+    });
+  });
+});