feat: migrate runtime backend to node server

.env.example

@@ -13,6 +13,21 @@ VITE_LLM_PROXY_BASE_URL="/api/llm"
 # Optional frontend override for the local custom-world scene image proxy path.
 VITE_SCENE_IMAGE_PROXY_BASE_URL="/api/custom-world/scene-image"
 
+# Local Node backend address and target used by Vite's dev proxy for runtime API routes.
+NODE_SERVER_ADDR=":8081"
+NODE_SERVER_TARGET="http://127.0.0.1:8081"
+
+# Local Caddy upstream target used for dist-based testing.
+CADDY_API_UPSTREAM="http://127.0.0.1:8081"
+
+# Node backend SQLite database path.
+SQLITE_PATH=""
+
+# Node backend JWT settings.
+JWT_SECRET="CHANGE_ME_FOR_PRODUCTION"
+# 当前默认签发永久 JWT，此字段暂未使用，后续如果恢复有限期 token 再启用。
+JWT_EXPIRES_IN="7d"
+
 # Model name for chat completions.
 VITE_LLM_MODEL="doubao-1-5-pro-32k-character-250715"