Add Admin Dashboard to Lovable App

Add a comprehensive admin dashboard to my Lovable app.

REQUIREMENTS:
1. Create an /admin route group that is only accessible to users with role="admin" in their profile. Redirect non-admins to the home page with an error toast.
2. Dashboard overview page with KPI cards: total users, new users (last 7 days), total revenue, active subscriptions. Use Recharts for a line chart of signups over the last 30 days.
3. User management page: searchable/sortable table of all users with columns for name, email, role, signup date, subscription status. Actions: view profile, change role, suspend/activate, delete.
4. Content management page: CRUD interface for managing the main content type (posts, products, listings, etc.). Table view with inline editing, bulk actions (delete, publish/unpublish), and a create/edit form.
5. Settings page: manage site-wide settings (site name, description, contact email, social links) stored in a "site_settings" table.
6. Activity log page: recent admin actions (user changes, content edits, setting updates) stored in an "admin_audit_log" table.

DATABASE:
- Add "role" column to profiles table (default: "user", options: "user", "admin")
- "site_settings" table: id, key, value, updated_at
- "admin_audit_log" table: id, admin_user_id, action, target_type, target_id, details (jsonb), created_at
- RLS: Only admins can read/write admin tables

SECURITY:
- Check role server-side, not just client-side.
- Log all admin actions to the audit trail.
- Require re-authentication for destructive actions (delete user, change roles).