fix(tests): add isDark and setTheme to PlaceholderScreen test mock

Align ThemeContext mock with the full contract to prevent future
test failures when components access isDark or setTheme.

Co-authored-by: Bill Chirico <undefined@users.noreply.github.com>

Author: github-actions[bot]

__tests__/components/program/PlaceholderScreen.test.tsx

@@ -27,6 +27,8 @@ const mockTheme = {
 jest.mock('@/contexts/ThemeContext', () => ({
   useTheme: () => ({
     theme: mockTheme,
+    isDark: false,
+    setTheme: jest.fn(),
   }),
 }));