Implement comprehensive dark/light mode overhaul for admin panel

- Refactor color palette in `ui-design-spec.md` to utilize CSS variables exclusively, eliminating fixed hex values and Tailwind utility classes.
- Complete dark mode implementation in `uiStore.ts`, ensuring proper theme application via `applyTheme()` and `applyBrand()`.
- Create `admin-theme-dark-light-audit.md` to document the transition process, outlining issues with inline styles and fixed colors.
- Introduce `theme-tokens.test.ts` to enforce rules against fixed hex colors and ensure compliance with the design system.
- Update various components and styles to replace inline styles and fixed colors with CSS variables, ensuring consistent theming across light and dark modes.
- Ensure all changes maintain visual integrity in both light and dark modes, with a focus on accessibility and contrast standards.

assets/admin/components/SessionStepper.test.tsx

@@ -23,9 +23,9 @@ describe('SessionStepper', () => {
 
   it('کانکتور گام‌های طی‌شده بنفش و بقیه خاکستری', () => {
     render(<SessionStepper steps={STEPS} activeStep={1} />);
-    // jsdom رنگ hex را به rgb نرمال می‌کند
-    expect(screen.getByTestId('step-connector-1').style.background).toContain('rgb(85, 89, 206)');
-    expect(screen.getByTestId('step-connector-2').style.background).toContain('rgb(234, 234, 240)');
+    // رنگ‌ها از توکن‌های تم می‌آیند تا در دارک‌مود هم درست باشند
+    expect(screen.getByTestId('step-connector-1').style.background).toContain('var(--primary)');
+    expect(screen.getByTestId('step-connector-2').style.background).toContain('var(--surface-2)');
   });
 
   it('استپر خالی: بدون کرش و بدون کانکتور', () => {