feat: enhance agent management and validation logic

- Updated AGENTS.md to clarify agent account restrictions and permissions.
- Implemented checks in AgentNodeAdminUserStoreController and AgentNodeRoleStoreController to restrict admin user and role creation to the agent's own node.
- Enhanced validation in AdminPlayerStoreController and AdminPlayerUpdateController to enforce credit limit and rebate rate rules based on player funding mode.
- Refactored various request classes to utilize shared admin account field rules for consistency.
- Improved error handling in services related to credit allocation and rebate limits to ensure proper validation and messaging.

tests/Feature/AdminAgentNodeApiTest.php

@@ -58,13 +58,8 @@ function grantAgentOperatorRole(AdminUser $admin, AgentNode $agent, bool $manage
         ]);
     }
 
-    DB::table('admin_user_site_roles')->insert([
-        'admin_user_id' => $admin->id,
-        'site_id' => (int) $agent->admin_site_id,
-        'role_id' => $roleId,
-        'granted_at' => $now,
-    ]);
-
+    // Only bind to agent node, not site roles
+    // This ensures the user is treated as an agent account
     DB::table('admin_user_agents')->insert([
         'admin_user_id' => $admin->id,
         'agent_node_id' => (int) $agent->id,