fix: use different way to start server in tanstack example

[KyleAMathews]

forever is getting this error:

> forever start src/server/app.js

warn:    --minUptime not set. Defaulting to: 1000ms
warn:    --spinSleepTime not set. Your script will exit if it does not stay up for at least 1000ms
info:    Forever processing file: src/server/app.js
(node:62642) Warning: Accessing non-existent property 'padLevels' of module exports inside circular dependency
(Use `node --trace-warnings ...` to show where the warning was created)
(node:62642) Warning: Accessing non-existent property 'padLevels' of module exports inside circular dependency

Forever hasn't been released in 3 years so I guess has accumulated enough bitrot to die.

We'll use concurrently instead.