Support subdirectory deployment and fix API path handling (#311)

* feat: support subdirectory deployment (NEXT_PUBLIC_BASE_PATH)

* removed unwanted check and fix favicon issue

* Use getAssetUrl for manifest assets to avoid undefined NEXT_PUBLIC_BASE_PATH

* Add validation warning for NEXT_PUBLIC_BASE_PATH format

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

docker-compose.yml

@@ -7,6 +7,11 @@ services:
       context: .
       args:
         - NEXT_PUBLIC_DRAWIO_BASE_URL=http://localhost:8080
+        # Uncomment below for subdirectory deployment
+        # - NEXT_PUBLIC_BASE_PATH=/nextaidrawio
     ports: ["3000:3000"]
     env_file: .env
+    environment:
+      # For subdirectory deployment, uncomment and set your path:
+      # NEXT_PUBLIC_BASE_PATH: /nextaidrawio
     depends_on: [drawio]