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/inventory/InventoryActionsMenu.tsx

@@ -55,7 +55,7 @@ export default function InventoryActionsMenu({ item, onEdit, onDelete }: Props)
         style={{
           display: 'flex', alignItems: 'center', gap: 4, cursor: 'pointer',
           borderRadius: 6, padding: '4px 8px', background: 'none',
-          color: '#5559ce', fontSize: 12, fontWeight: 500,
+          color: 'var(--primary)', fontSize: 12, fontWeight: 500,
         }}
       >
         <EllipsisHorizontalCircleIcon style={{ width: 18, height: 18 }} />