feat: Refactor code structure and optimize performance across multiple modules

mobile-apps/staff-app/backend_architecture.mermaid

@@ -0,0 +1,37 @@
+graph TD
+    subgraph Flutter App
+        A[Flutter UI]
+        B[GraphQL Client]
+        C[Firebase SDK]
+    end
+
+    subgraph Backend
+        D[GraphQL Server]
+        E[Firebase]
+    end
+
+    subgraph Firebase
+        F[Firebase Auth]
+        G[Firebase Firestore]
+        H[Firebase Storage]
+        I[Firebase Cloud Functions]
+        J[Firebase Cloud Messaging]
+        K[Firebase Remote Config]
+    end
+
+    A --> B;
+    A --> C;
+
+    B --> D;
+    C --> F;
+    C --> J;
+    C --> K;
+
+    D --> G;
+    D --> H;
+    D --> I;
+    D --> F;
+
+    I --> G;
+    I --> H;
+    I --> J;