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/DashboardPage.tsx

@@ -1,6 +1,6 @@
 import { useState, useEffect } from 'react'
 import { Link } from 'react-router-dom'
-import { Users, TreePine, CreditCard, Activity, TrendingUp } from 'lucide-react'
+import { Users, TreePine, CreditCard, Activity, TrendingUp, Building2 } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { PageHeader } from '@/components/admin'
 import { adminApi } from '@/api/admin'
@@ -43,7 +43,7 @@ export function DashboardPage() {
   }, [])
 
   const quickLinks = [
-    { to: '/admin/users', label: 'Manage Users', icon: Users },
+    { to: '/admin/accounts', label: 'Manage Accounts', icon: Building2 },
     { to: '/admin/plan-limits', label: 'Plan Limits', icon: TrendingUp },
     { to: '/admin/feature-flags', label: 'Feature Flags', icon: Activity },
     { to: '/admin/audit-logs', label: 'Audit Logs', icon: Activity },