fix: resolve CouchDB connection issues in backend tests

- Add jest.preSetup.js to mock modules before loading
- Skip CouchDB initialization during test environment
- Update browserslist data to fix deprecation warnings
- Improve error handling test infrastructure
- Fix fs.F_OK deprecation warning via dependency update

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Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

backend/server.js

@@ -60,12 +60,15 @@ const apiLimiter = rateLimit({
 
 // Database Connection
 // CouchDB (primary database)
-couchdbService.initialize()
-  .then(() => console.log("CouchDB initialized"))
-  .catch((err) => {
-    console.log("CouchDB initialization error:", err);
-    process.exit(1); // Exit if CouchDB fails to initialize since it's the primary database
-  });
+// Skip initialization during testing
+if (process.env.NODE_ENV !== 'test') {
+  couchdbService.initialize()
+    .then(() => console.log("CouchDB initialized"))
+    .catch((err) => {
+      console.log("CouchDB initialization error:", err);
+      process.exit(1); // Exit if CouchDB fails to initialize since it's the primary database
+    });
+}
 
 // Socket.IO Authentication Middleware
 io.use(socketAuth);
@@ -165,6 +168,9 @@ if (require.main === module) {
   });
 }
 
+// Export app and server for testing
+module.exports = { app, server, io };
+
 // Graceful shutdown
 process.on("SIGTERM", async () => {
   console.log("SIGTERM received, shutting down gracefully");