docs: add missing env file flag to frontend start command

CONTRIBUTING.md

@@ -69,5 +69,5 @@ We are using [Playwright](https://playwright.dev) for end-to-end testing.
 
 The tests can be run like this:
 1. Start the backend normally
-2. Start the frontend in production mode with `npm run build && node build/index.js`
+2. Start the frontend in production mode with `npm run build && node --env-file=.env build/index.js`
 3. Run the tests with `npm run test`

docs/docs/setup/upgrading.md

@@ -37,7 +37,7 @@ docker compose up -d
    cd ../frontend
    npm install
    npm run build
-   pm2 start build/index.js --name pocket-id-frontend
+   pm2 start --name pocket-id-frontend --node-args="--env-file .env" build/index.js
 
    # Optional: Start Caddy (You can use any other reverse proxy)
    cd ..