Add test coverage for remaining API routes

[Copilot]

Only 1 of 8 API routes had test coverage (branch.test.ts). This PR adds tests for the remaining 7 routes, bringing coverage from 6 to 48 tests.

Changes

• Added reset functions to product, supplier, headquarters, delivery, order, orderDetail, and orderDetailDelivery routes for test isolation
• Created test files for each route following the existing vitest + supertest pattern
• Test coverage includes CRUD operations (POST/GET/PUT/DELETE) and 404 error handling

Pattern

Each test file follows the established pattern:

describe('Product API', () => {
    beforeEach(() => {
        app = express();
        app.use(express.json());
        app.use('/products', productRouter);
        resetProducts();
    });

    it('should create a new product', async () => { /* ... */ });
    it('should get all products', async () => { /* ... */ });
    it('should get a product by ID', async () => { /* ... */ });
    it('should update a product by ID', async () => { /* ... */ });
    it('should delete a product by ID', async () => { /* ... */ });
    it('should return 404 for non-existing product', async () => { /* ... */ });
});

All 48 tests pass. No security issues detected by CodeQL.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Test Issue</issue_title>
<issue_description>this is a test</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Test Issue #1

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