FRONTEND: Build Query String (Utility Function)

**Description:**
Create a function that builds a query string from an object. This complements `parseQueryParams`.

**Tasks:**

* Add `lib/utils/buildQueryString.ts`.
* Accept object input and return a string.
* Handle nested values gracefully.
* Write unit tests.

**Acceptance Criteria:**

* `buildQueryString({ page: 2, limit: 10 })` → `"?page=2&limit=10"`.
* Handles empty objects → `""`.