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/pages/LoginPage.tsx

@@ -227,7 +227,7 @@ export default function LoginPage() {
                 flex: 1, padding: '8px 0', borderRadius: 8, border: 'none', cursor: 'pointer',
                 fontFamily: 'inherit', fontSize: 13, fontWeight: 600, transition: 'all 0.15s',
                 background: mode === m ? 'var(--primary)' : 'transparent',
-                color: mode === m ? '#fff' : 'var(--text-2)',
+                color: mode === m ? 'var(--on-primary)' : 'var(--text-2)',
               }}>
                 {m === 'password' ? 'رمز عبور' : 'ورود با پیامک'}
               </button>