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/InvoiceSummaryModal.tsx

@@ -103,7 +103,7 @@ export default function InvoiceSummaryModal({ invoiceUuid, onClose }: { invoiceU
             rows={[[
               formatDate(session?.session_at ?? inv.issued_at),
               session?.paid_at ? formatDate(session.paid_at) : paid ? formatDate(inv.issued_at) : '—',
-              <span style={{ color: remaining > 0 ? '#d32f2f' : '#388e3c', fontWeight: 600 }}>{statusLabel}</span>,
+              <span style={{ color: remaining > 0 ? 'var(--danger)' : 'var(--success)', fontWeight: 600 }}>{statusLabel}</span>,
             ]]}
           />
           {(inv.base_insurance_name || inv.service_category_label) && (
@@ -168,7 +168,7 @@ export default function InvoiceSummaryModal({ invoiceUuid, onClose }: { invoiceU
             cols={['مبلغ کل پرداخت شده', 'مبلغ باقی مانده']}
             rows={[[
               formatRial(paidAmount),
-              <span style={{ color: remaining > 0 ? '#d32f2f' : '#388e3c', fontWeight: 600 }}>{formatRial(remaining)}</span>,
+              <span style={{ color: remaining > 0 ? 'var(--danger)' : 'var(--success)', fontWeight: 600 }}>{formatRial(remaining)}</span>,
             ]]}
           />
         </div>