rename lila to lila.sh

Works around a weird scalac(?) bug where compilation fails when LANGUAGE
is not set to `en_US`, on some environments.

To reproduce:
```
export LANGUAGE=fr
./lila clean
./lila compile
```

Stacktrace:
https://gist.github.com/ornicar/4a7b136d2220f4c1fd43e920956f67b4

The bug was reproduced on a Debian GNU/Linux 12 (bookworm) x86_64.
It could not be reproduced on NixOS 24.11 (Vicuna) x86_64