fix(model): land #30932 auth-profile @ parsing for /model (@haosenwang1018)

Landed from contributor PR #30932 by @haosenwang1018.

Co-authored-by: haosenwang1018 <haosenwang1018@users.noreply.github.com>

src/agents/model-ref-profile.test.ts

@@ -46,4 +46,11 @@ describe("splitTrailingAuthProfile", () => {
       model: "provider/foo@bar/baz",
     });
   });
+
+  it("uses first @ after last slash for email-based auth profiles", () => {
+    expect(splitTrailingAuthProfile("flash@google-gemini-cli:test@gmail.com")).toEqual({
+      model: "flash",
+      profile: "google-gemini-cli:test@gmail.com",
+    });
+  });
 });