Add upsert tournament team write API

Closes #3294

app/features/api-public/api-action-wrapper.server.ts

@@ -7,6 +7,7 @@ import type { ActionFunction, ActionFunctionArgs } from "react-router";
  * The existing actions use:
  * - `successToast(message)` which returns `redirect("?__success=message")`
  * - `errorToastIfFalsy/errorToastIfErr` which throw `redirect("?__error=message")`
+ * - `{ fieldErrors }` returns for form validation failures
  */
 export async function wrapActionForApi(
 	actionFn: ActionFunction,
@@ -19,6 +20,19 @@ export async function wrapActionForApi(
 			return new Response(null, { status: 200 });
 		}
 
+		if (response && typeof response === "object" && "fieldErrors" in response) {
+			return new Response(
+				JSON.stringify({
+					error: "Validation failed",
+					fieldErrors: response.fieldErrors,
+				}),
+				{
+					status: 400,
+					headers: { "Content-Type": "application/json" },
+				},
+			);
+		}
+
 		return response as Response;
 	} catch (e) {
 		if (e instanceof Response && e.status === 302) {