fix: inline ErrorDetail in ErrorResponse to fix Spectral ref resolution

Spectral resolves nested $ref paths relative to the referencing file
rather than the referenced file, causing ENOENT when response files
reference ErrorResponse.yaml which then $refs ErrorDetail.yaml.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: vdusek

apify-api/openapi/components/schemas/common/ErrorResponse.yaml

@@ -4,4 +4,11 @@ required:
 type: object
 properties:
   error:
-    $ref: ./ErrorDetail.yaml
+    type: object
+    properties:
+      type:
+        type: string
+        description: Machine-processable error type identifier.
+      message:
+        type: string
+        description: Human-readable error message describing what went wrong.