test: Added test files
Description: This MR improves the frontend test suite on test_files by adding targeted tests for the files that were still under-covered in the previous coverage
report: The main focus was on replacing smoke-only coverage with behavior-driven coverage:
- added entrypoint coverage for src/main.tsx
- added direct CardGrid tests to cover conditional header and card rendering branches
- strengthened ScrollToTop tests to cover the missing hash-target branch
- replaced simple render checks on the pharmacogenomics and WGS pages with accordion interaction tests