refactor: reorganize project into monorepo with frontend scaffolding

Convert project from single backend to monorepo structure with separate
frontend (Vue 3 + TypeScript + Vite) and backend directories. Updates
all configuration files and build system to support both workspaces.

Ref: T007 (specs/001-modbus-relay-control)

package.json

@@ -0,0 +1,22 @@
+{
+  "name": "frontend",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vue-tsc -b && vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "vue": "^3.5.24"
+  },
+  "devDependencies": {
+    "@types/node": "^24.10.1",
+    "@vitejs/plugin-vue": "^6.0.1",
+    "@vue/tsconfig": "^0.8.1",
+    "typescript": "~5.9.3",
+    "vite": "^7.2.4",
+    "vue-tsc": "^3.1.4"
+  }
+}