feat(settings): add autoSaveSettings for lightweight auto-save

Add optimized auto-save function for General tab settings.
- Add autoSaveSettings method for non-destructive auto-save
- Only trigger system APIs when values actually change
- Avoid unnecessary auto-launch and plugin config updates
- Update tests to cover new functionality

tests/hooks/useDirectorySettings.test.tsx

@@ -84,6 +84,7 @@ describe("useDirectorySettings", () => {
       appConfig: "/override/app",
       claude: "/remote/claude",
       codex: "/remote/codex",
+      gemini: "/remote/codex", // Gemini 使用 codex 作为默认
     });
   });