refactor: clean up unused code and simplify imports

- Remove unused imports and variables across 35 files
- Simplify component logic and remove dead code
- Clean up test files by removing unnecessary setup
- Streamline CI workflow configuration

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/components/__tests__/TopBar.test.tsx

@@ -6,7 +6,6 @@ import TopBar from '@/components/TopBar';
 import { RouterProvider } from '@/providers/RouterProvider';
 import { ThemeModeProvider } from '@/providers/ThemeModeProvider';
 
-// matchMedia must be mocked before ThemeModeProvider is imported
 Object.defineProperty(window, 'matchMedia', {
   writable: true,
   value: vi.fn().mockImplementation((query: string) => ({