:gear: tweak env var name for vite pick-up

frontend/.env.sample

 VITE_PUBNUB_PUBLISH_KEY=pub-a-123467890-123467890
 VITE_PUBNUB_SUBSCRIBE_KEY=sub-a-123467890-123467890
-API_HOST=localhost
-API_PORT=3001
+VITE_API_HOST=localhost
+VITE_API_PORT=3001

frontend/src/utils/db.js

-const domain = import.meta.env.API_HOST
-const port = import.meta.env.API_PORT
+const domain = import.meta.env.VITE_API_HOST
+const port = import.meta.env.VITE_API_PORT
 const httpProtocol = `http`
 const prefix = 'api'
 const remote = `${httpProtocol}://${domain}:${port}/${prefix}`