feat: extract admin account management rework from PR 124 (#138)

* feat: reorganize admin panel around accounts

* feat: expand admin customer account controls

* feat: add admin account detail management

* fix: remove unused admin account icon import

* refactor: design critique fixes for account pages

- Admin accounts: replace dense card grid with compact DataTable
- Account settings: remove redundant hero card, stat grid, header pills
- Fix bg-accent (orange) misuse on decorative elements across 7 files
- Add ConfirmButton for destructive actions (deactivate, remove member)
- Replace single-field modals with inline editing (plan, trial)
- Add contextual help: display code tooltip, improved empty states
- Non-owner aside explanation for hidden owner-only sections
- Admin sidebar: group 11 items into 5 labeled sections
- Rename UsersPage.tsx → AccountsPage.tsx to match route
- Fix border radius consistency, hide zero-count badges

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: use get_admin_db for all new admin account endpoints

All admin endpoints query across tenants without a tenant context.
get_db (app-role, subject to RLS) was never imported and would crash
at runtime — replace all 6 occurrences with get_admin_db (BYPASSRLS).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/admin/Pagination.tsx

@@ -43,7 +43,7 @@ export function Pagination({ page, totalPages, total, pageSize, onPageChange }:
         <button
           onClick={() => onPageChange(page - 1)}
           disabled={page <= 1}
-          className={cn(btnBase, 'px-2 text-muted-foreground hover:bg-accent hover:text-foreground')}
+          className={cn(btnBase, 'px-2 text-muted-foreground hover:bg-elevated hover:text-foreground')}
         >
           <ChevronLeft className="h-4 w-4" />
         </button>
@@ -59,7 +59,7 @@ export function Pagination({ page, totalPages, total, pageSize, onPageChange }:
                 'px-2',
                 p === page
                   ? 'bg-primary text-white'
-                  : 'text-muted-foreground hover:bg-accent hover:text-foreground'
+                  : 'text-muted-foreground hover:bg-elevated hover:text-foreground'
               )}
             >
               {p}
@@ -69,7 +69,7 @@ export function Pagination({ page, totalPages, total, pageSize, onPageChange }:
         <button
           onClick={() => onPageChange(page + 1)}
           disabled={page >= totalPages}
-          className={cn(btnBase, 'px-2 text-muted-foreground hover:bg-accent hover:text-foreground')}
+          className={cn(btnBase, 'px-2 text-muted-foreground hover:bg-elevated hover:text-foreground')}
         >
           <ChevronRight className="h-4 w-4" />
         </button>