Add monorepo setup with Turborepo and Web client

- Add pnpm workspace and Turborepo configuration
- Extract Gateway SDK to packages/sdk as independent package
- Add Next.js + shadcn Web client in apps/web
- Update root package.json with turbo scripts

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/package.json

@@ -0,0 +1,35 @@
+{
+  "name": "@multica/web",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "next dev --turbopack",
+    "build": "next build",
+    "start": "next start",
+    "lint": "eslint"
+  },
+  "dependencies": {
+    "@multica/sdk": "workspace:*",
+    "@base-ui/react": "^1.1.0",
+    "@hugeicons/core-free-icons": "^3.1.1",
+    "@hugeicons/react": "^1.1.4",
+    "class-variance-authority": "^0.7.1",
+    "clsx": "^2.1.1",
+    "next": "16.1.6",
+    "react": "19.2.3",
+    "react-dom": "19.2.3",
+    "shadcn": "^3.7.0",
+    "tailwind-merge": "^3.4.0",
+    "tw-animate-css": "^1.4.0"
+  },
+  "devDependencies": {
+    "@tailwindcss/postcss": "^4",
+    "@types/node": "^20",
+    "@types/react": "^19",
+    "@types/react-dom": "^19",
+    "eslint": "^9",
+    "eslint-config-next": "16.1.6",
+    "tailwindcss": "^4",
+    "typescript": "^5"
+  }
+}