feat(utils): add generic buildQueryString utility

- Add type-safe buildQueryString function to /utils
- Support primitives, arrays, and optional values
- Proper URL encoding for special characters
- Add comprehensive tests (25 test cases, all passing)
- Update Google Fonts API client to use shared utility
- Update Fontshare API client to use shared utility
- Export utility from /utils/index.ts

Benefits:
- DRY - Single source of truth for query string logic
- Type-safe - Proper TypeScript support with QueryParams type
- Tested - Comprehensive test coverage
- Maintainable - One place to fix bugs

src/shared/utils/index.ts

@@ -0,0 +1,9 @@
+/**
+ * Shared utility functions
+ */
+
+export { buildQueryString } from './buildQueryString';
+export type {
+    QueryParams,
+    QueryParamValue,
+} from './buildQueryString';