Rename company-scoped Users to Members throughout

Complete rename across backend and frontend:
- Controller: Company/Users/UsersController -> Company/Members/MembersController
- Service: UserService -> MemberService
- Requests: UserRequest -> MemberRequest, DeleteUserRequest -> DeleteMemberRequest
- API routes: /api/v1/users -> /api/v1/members (company-scoped only)
- Sidebar menu: "Users" -> "Members"
- Frontend: views/users -> views/members, stores/users -> stores/members
- Router: users.index -> members.index, /admin/users -> /admin/members
- i18n: new "members" section with invitation-related keys
- Tests: UserTest -> MemberTest

Admin/super-admin Users (system-wide user management) remains unchanged.

config/invoiceshelf.php

@@ -352,11 +352,11 @@ return [
             ] : []
         ),
         [
-            'title' => 'navigation.users',
+            'title' => 'navigation.members',
             'group' => 3,
-            'link' => '/admin/users',
+            'link' => '/admin/members',
             'icon' => 'UsersIcon',
-            'name' => 'Users',
+            'name' => 'Members',
             'owner_only' => true,
             'ability' => '',
             'model' => '',