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/ClinicDetailPage.tsx

@@ -631,7 +631,7 @@ export default function ClinicDetailPage() {
                         borderRadius: '50%', background: 'var(--primary)', border: '2px solid var(--surface)',
                         display: 'flex', alignItems: 'center', justifyContent: 'center', cursor: 'pointer',
                       }}>
-                      <CameraIcon style={{ width: 12, height: 12, color: '#fff' }} />
+                      <CameraIcon style={{ width: 12, height: 12, color: 'var(--on-primary)' }} />
                     </button>
                     <input ref={logoInputRef} type="file" accept="image/*" style={{ display: 'none' }}
                       onChange={e => e.target.files?.[0] && handleLogoUpload(e.target.files[0])} />