Add reusable tools and assistant bindings

- Introduce a new `Tool` model and `AssistantToolBinding` for managing reusable tools within the application.
- Implement CRUD operations for tools in the new `tools` route, allowing for the creation, retrieval, updating, and deletion of tools.
- Update the `Assistant` model to include a list of tool IDs, enabling assistants to utilize these tools.
- Enhance the backend routes to synchronize tool bindings with assistants, ensuring proper management of tool associations.
- Add frontend components for tool management, including a tool picker in the assistant configuration, improving user experience in tool selection.
- Create a mobile call page to facilitate video calls, integrating camera and microphone selection for enhanced communication capabilities.
- Update API definitions to include tool-related types and operations, ensuring consistency across the application.
- Add a migration script to create the necessary database tables for tools and bindings, supporting the new functionality.

frontend/src/components/auth/AuthGate.tsx

@@ -11,6 +11,7 @@ export function AuthGate({ children }: { children: ReactNode }) {
   const router = useRouter();
   const { user, loading } = useAuth();
   const isLoginPage = pathname === "/login";
+  const isCallPage = pathname.startsWith("/call/");
 
   useEffect(() => {
     if (!loading && !user && !isLoginPage) {
@@ -30,5 +31,10 @@ export function AuthGate({ children }: { children: ReactNode }) {
     );
   }
 
+  // 手机通话预览沿用登录态，但不显示管理台导航框架。
+  if (isCallPage) {
+    return <>{children}</>;
+  }
+
   return <AppShell>{children}</AppShell>;
 }