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/pages/admin/UserDetailPage.tsx

@@ -177,7 +177,7 @@ export function UserDetailPage() {
     try {
       await adminApi.hardDeleteUser(userId)
       toast.success('User permanently deleted')
-      navigate('/admin/users')
+      navigate('/admin/accounts')
     } catch (err: unknown) {
       if (err && typeof err === 'object' && 'response' in err) {
         const axiosErr = err as { response?: { data?: { detail?: string } } }
@@ -207,8 +207,8 @@ export function UserDetailPage() {
         title="User not found"
         description="This user may have been removed or is unavailable."
         action={(
-          <Button variant="secondary" onClick={() => navigate('/admin/users')}>
-            Back to Users
+          <Button variant="secondary" onClick={() => navigate('/admin/accounts')}>
+            Back to Accounts
           </Button>
         )}
       />
@@ -223,7 +223,7 @@ export function UserDetailPage() {
       {/* Header */}
       <div className="flex items-center gap-4">
         <button
-          onClick={() => navigate('/admin/users')}
+          onClick={() => navigate('/admin/accounts')}
           className="rounded-md border border-border p-2 text-muted-foreground hover:bg-accent hover:text-foreground"
         >
           <ArrowLeft className="h-4 w-4" />