feat(FN-3175): document global tool output persistence setting in settings

Added documentation for the global tool output persistence setting to the settings reference guide.

Fusion-Task-Id: FN-3175

packages/core/src/__tests__/settings-parity.test.ts

@@ -55,6 +55,8 @@ describe("settings key parity", () => {
     expect(isGlobalSettingsKey("researchGlobalDefaults")).toBe(true);
     expect(isProjectSettingsKey("themeMode")).toBe(false);
     expect(isGlobalSettingsKey("remoteAccess")).toBe(true);
+    expect(isGlobalSettingsKey("persistAgentToolOutput")).toBe(true);
+    expect(isProjectSettingsKey("persistAgentToolOutput")).toBe(false);
     expect(isGlobalSettingsKey("researchSettings")).toBe(false);
   });