fix(api): map upstream timeouts to 504 responses

ts/containers/base-container.ts

@@ -24,6 +24,13 @@ export type TModelPullProgress = (progress: {
   percent?: number;
 }) => void;
 
+export class UpstreamTimeoutError extends Error {
+  constructor(message: string = 'Upstream request timed out') {
+    super(message);
+    this.name = 'UpstreamTimeoutError';
+  }
+}
+
 /**
  * Abstract base class for AI model containers
  */
@@ -181,6 +188,11 @@ export abstract class BaseContainer {
       });
 
       return response;
+    } catch (error) {
+      if (error instanceof Error && error.name === 'AbortError') {
+        throw new UpstreamTimeoutError();
+      }
+      throw error;
     } finally {
       clearTimeout(timeoutId);
     }