chore(api): regenerate client for F1's new 400 responses

npm run gen:api after WP-68 F1 — draft-sync and submit now document their
document-ownership 400 ProblemDetails response.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/swagger.json

@@ -643,6 +643,16 @@
           "204": {
             "description": "No Content"
           },
+          "400": {
+            "description": "Bad Request",
+            "content": {
+              "application/problem+json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ProblemDetails"
+                }
+              }
+            }
+          },
           "404": {
             "description": "Not Found"
           }
@@ -718,6 +728,16 @@
               }
             }
           },
+          "400": {
+            "description": "Bad Request",
+            "content": {
+              "application/problem+json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ProblemDetails"
+                }
+              }
+            }
+          },
           "409": {
             "description": "Conflict",
             "content": {