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/ActionMenu.tsx

@@ -54,7 +54,7 @@ export function ActionMenu({ items }: ActionMenuProps) {
         onClick={() => setOpen(!open)}
         className={cn(
           'rounded-md p-1.5 text-muted-foreground transition-colors',
-          'hover:bg-accent hover:text-foreground'
+          'hover:bg-elevated hover:text-foreground'
         )}
       >
         <MoreHorizontal className="h-4 w-4" />
@@ -81,7 +81,7 @@ export function ActionMenu({ items }: ActionMenuProps) {
                 'disabled:opacity-50 disabled:pointer-events-none',
                 item.destructive
                   ? 'text-red-400 hover:bg-red-400/10'
-                  : 'text-muted-foreground hover:bg-accent'
+                  : 'text-muted-foreground hover:bg-elevated'
               )}
             >
               {item.icon}