fix(admin): AdminShell brands type must include logo_url (AdminSidebar requires it)

The plan's AdminShell type for the brands prop was missing the
logo_url field that AdminSidebar requires. The plan's spec example
is corrected to include the field, and the code is updated to match
(so a consumer of AdminShell is forced to pass logo_url, matching
the contract AdminSidebar expects).

Also corrects three other plan discrepancies found while implementing
Tasks 1.7-1.12:
- Task 1.12: existing EmptyState.tsx is in active use; reuse it
  instead of creating a duplicate.
- Task 1.12: CardList.tsx had a redundant 'export { CardListItem }'
  after the function was already exported, which is a TS syntax error.
  Removed the redundant line.
- Plan narrative now reflects all three corrections.

TypeScript is clean; full test suite still at 166/3 (the 3 failures
are the pre-existing getAdminUser tests, unchanged).

src/components/admin/AdminShell.tsx

@@ -8,7 +8,7 @@ interface AdminShellProps {
   userRole: string | null;
   brandIds?: string[];
   activeBrandId?: string | null;
-  brands: { id: string; name: string; slug: string }[];
+  brands: { id: string; name: string; slug: string; logo_url: string | null }[];
   enabledAddons?: Record<string, boolean>;
   children: ReactNode;
 }