Add super-admin Administration section and restructure global vs company settings

- Add Administration sidebar section (super-admin only) with Companies, Users, and Global Settings pages
- Add super-admin middleware, controllers, and API routes under /api/v1/super-admin/
- Allow super-admins to manage all companies and users across tenants
- Add user impersonation with short-lived tokens, audit logging, and UI banner
- Move system-level settings (Mail, PDF, Backup, Update, File Disk) from per-company to Administration > Global Settings
- Convert save_pdf_to_disk from CompanySetting to global Setting
- Add per-company mail configuration overrides (optional, falls back to global)
- Add CompanyMailConfigService to apply company mail config before sending emails

app/Http/Resources/UserResource.php

@@ -32,6 +32,7 @@ class UserResource extends JsonResource
             'updated_at' => $this->updated_at,
             'avatar' => $this->avatar,
             'is_owner' => $this->isOwner(),
+            'is_super_admin' => $this->isSuperAdmin(),
             'roles' => $this->roles,
             'formatted_created_at' => $this->formattedCreatedAt,
             'currency' => $this->when($this->currency()->exists(), function () {