Update package dependencies and documentation for LemonSpace v1.5

- Added `next-intl` dependency to `package.json` for internationalization support.
- Updated `pnpm-lock.yaml` to reflect the new dependency and its version.
- Revised LemonSpace Manifest and PRD to version 1.5, including updates to authentication methods and new features for offline sync and canvas management.

package.json

@@ -31,6 +31,7 @@
     "jszip": "^3.10.1",
     "lucide-react": "^1.6.0",
     "next": "16.2.1",
+    "next-intl": "^4.8.4",
     "next-themes": "^0.4.6",
     "optional": "^0.1.4",
     "radix-ui": "^1.4.3",