refactor(app): rewrite application with Nuxt 4, Pinia, and TailwindCSS

This commit replaces the original vanilla JavaScript implementation with a modern frontend stack. The entire application has been rewritten to improve maintainability, developer experience, and leverage modern
web technologies.

Key changes include:
- Replaced plain HTML, CSS, and JS with a Nuxt 4 project structure.
- Migrated state management from a global state object to a Pinia store for better organization and reactivity.
- Rebuilt the UI with Vue 3 components and styled with TailwindCSS.
- Changed the primary persistence mechanism from manual file I/O to automatic LocalStorage saving, while retaining import/export functionality.
- All core features, including drag-and-drop, task management, and the import/merge diffing logic, have been ported to the new architecture.

package.json

@@ -0,0 +1,28 @@
+{
+  "name": "open-kanban-nuxt",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "nuxt dev",
+    "build": "nuxt build",
+    "preview": "nuxt preview",
+    "lint": "echo 'no lint configured'"
+  },
+  "dependencies": {
+    "nuxt": "^4.0.0",
+    "pinia": "^2.1.7",
+    "@pinia/nuxt": "^0.5.1",
+    "zod": "^3.23.8",
+    "@vueuse/core": "^11.0.0"
+  },
+  "devDependencies": {
+    "typescript": "^5.6.3",
+    "@nuxtjs/tailwindcss": "^6.11.4",
+    "tailwindcss": "^3.4.13",
+    "postcss": "^8.4.47",
+    "autoprefixer": "^10.4.19",
+    "@types/node": "^20.11.30"
+  }
+}
+