Add test fixture factory templates with faker.js

[PAMulligan]

Description

Add test fixture factory templates to the project setup that use `@faker-js/faker` for generating realistic test data. The `data-seeder` agent references faker.js patterns, but the generated project templates don't include factory utilities.

Why

Every API needs test data. Without factories, developers write ad-hoc test objects that are inconsistent and tedious to maintain. Factory templates give every generated project a standard pattern for creating test entities with realistic data.

Acceptance Criteria

• Add `@faker-js/faker` as a dev dependency in `setup-project.sh`
• Create a `tests/fixtures/factory.ts` template with:
  • A generic `createFactory()` function
  • A `userFactory` example using the generated user schema
  • Support for overrides (`userFactory({ name: 'Custom' })`)
  • Support for creating multiple (`userFactory.createMany(5)`)
• Create a `tests/fixtures/index.ts` that exports all factories
• Add an example usage in the generated health test or a new test file
• CI passes

Example

```typescript
// tests/fixtures/factory.ts
import { faker } from '@faker-js/faker';

export function userFactory(overrides?: Partial): NewUser {
return {
email: faker.internet.email(),
name: faker.person.fullName(),
...overrides,
};
}
```