Refactor code structure for improved readability and maintainability

package.json

@@ -7,6 +7,7 @@
   "scripts": {
     "start": "deno run --allow-all mod.ts server",
     "dev": "deno run --allow-all --watch mod.ts server --ephemeral",
+    "watch": "concurrently --kill-others --names \"BACKEND,UI\" --prefix-colors \"cyan,magenta\" \"deno run --allow-all --watch mod.ts server --ephemeral\" \"cd ui && pnpm run watch\"",
     "build": "cd ui && pnpm run build",
     "test": "deno test --allow-all"
   },
@@ -22,5 +23,8 @@
     "composer"
   ],
   "author": "Stack.Gallery",
-  "license": "MIT"
+  "license": "MIT",
+  "devDependencies": {
+    "concurrently": "^9.1.2"
+  }
 }