Critical fix start script for tanstack start addon

[SiddharthPant]

create-start-app creates a broken start script based on previous nitro plugin leftouts. This is creating lots of confusion whoever is trying to deploy on prod as server fails to start.

This PR adds a simple server based on srvx prod server which Tanstack start already internally uses in order to create a server script that runs for all node/bun/deno.

Please note, npm and bun do not need srvx to be added but pnpm requires explicit install, hence added it to package.json file as well which is anyways a good practise.

Modified the start script command from "node .output/server/index.mjs" to srvx --prod server.js.

Used srvx cli as it shows a bit more nice output logs than simple node server.js skips.

[SiddharthPant]

The team had a small discussion on discord and it was decided Nitro is the default we go with. Also a possible option during setup can be provided to skip nitro for no hosting minimal setup.
This PR is no longer required and underlying issue of prod server not running is already fixed.