chore: isolate frontend and backend via npm workspaces and @mmapp/contracts

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tsconfig.json

@@ -5,7 +5,7 @@
     "moduleResolution": "NodeNext",
     "lib": ["ES2022"],
     "outDir": "dist",
-    "rootDir": "..",
+    "rootDir": "src",
     "strict": true,
     "esModuleInterop": true,
     "skipLibCheck": true,