test(subagents): un-nest pin-parts cases from the custom-endpoint test

The two new pin-parts tests were inserted inside the custom-endpoint case.
They pass as nested subtests; keep them as siblings so a later edit cannot
accidentally drop the closing brace.

Author: vastsa

apps/desktop/test/subagent-models.test.mjs

@@ -56,6 +56,7 @@ test("a custom endpoint uses its display name instead of the generic vendor key"
     subagentModelPin({ vendorKey: "custom", name: "My Gateway" }, "local-model"),
     "My Gateway/local-model",
   );
+});
 
 test("every option the picker offers is a pin the editor will save", () => {
   // A custom endpoint's display name contains spaces, and the picker offers it.
@@ -96,7 +97,6 @@ test("a pin needs a provider half, a model half, and keeps its own slashes", ()
   assert.equal(subagentModelPinParts("/claude-haiku-4-5"), null);
   assert.equal(subagentModelPinParts("anthropic/"), null);
 });
-});
 
 test("the sheet lists configured models from enabled, credentialed providers", () => {
   const choices = subagentModelChoices([