feat(recipes): add recipe detail load function with 404 handling

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/(app)/recipes/[id]/page.server.test.ts

@@ -0,0 +1,57 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+vi.mock('$env/dynamic/private', () => ({
+	env: { BACKEND_URL: 'http://localhost:8080' }
+}));
+
+const mockGet = vi.fn();
+vi.mock('$lib/server/api', () => ({
+	apiClient: () => ({ GET: mockGet })
+}));
+
+describe('recipe detail page — load', () => {
+	let load: any;
+
+	beforeEach(async () => {
+		mockGet.mockReset();
+		vi.resetModules();
+		const mod = await import('./+page.server');
+		load = mod.load;
+	});
+
+	const mockRecipe = {
+		id: 'r1',
+		name: 'Spaghetti Bolognese',
+		serves: 4,
+		cookTimeMin: 30,
+		effort: 'Easy',
+		heroImageUrl: undefined,
+		ingredients: [
+			{ ingredientId: 'i1', name: 'Spaghetti', quantity: 200, unit: 'g' }
+		],
+		steps: [{ stepNumber: 1, instruction: 'Kochen' }],
+		tags: []
+	};
+
+	it('fetches recipe from GET /v1/recipes/{id}', async () => {
+		mockGet.mockResolvedValue({ data: mockRecipe, error: undefined });
+		await load({ fetch: vi.fn(), params: { id: 'r1' } } as any);
+		expect(mockGet).toHaveBeenCalledWith('/v1/recipes/{id}', expect.objectContaining({
+			params: { path: { id: 'r1' } }
+		}));
+	});
+
+	it('returns recipe data on success', async () => {
+		mockGet.mockResolvedValue({ data: mockRecipe, error: undefined });
+		const result = await load({ fetch: vi.fn(), params: { id: 'r1' } } as any);
+		expect(result.recipe.name).toBe('Spaghetti Bolognese');
+		expect(result.recipe.serves).toBe(4);
+	});
+
+	it('throws 404 error when API returns error', async () => {
+		mockGet.mockResolvedValue({ data: undefined, error: { status: 404 } });
+		await expect(
+			load({ fetch: vi.fn(), params: { id: 'nonexistent' } } as any)
+		).rejects.toMatchObject({ status: 404 });
+	});
+});