scala: Declare the scala toolchain in .tool-versions

scala/.gitignore

@@ -1,8 +1,7 @@
+# sbt build output
+target/
+
 # Metals / builds
 .bloop
 .bsp
 metals.sbt
-
-# Temp install of sbt
-sbt/
-*.zip

scala/.tool-versions

@@ -0,0 +1,2 @@
+java corretto-21
+sbt 1

scala/README.md

@@ -2,16 +2,26 @@
 
 Skeleton project for Scala.
 
+## Prerequisites
+
+The toolchain this project needs is declared in [`.tool-versions`](./.tool-versions):
+
+```
+java corretto-21
+sbt 1
+```
+
+Install those however you prefer, as long as they end up on your `PATH`. The quickest route is
+[mise](https://mise.jdx.dev/), which reads the file for you:
+
+```sh
+mise install
+```
+
 ## Usage
-- `./script/setup` to install dependencies
-- `./script/test` to run the tests
-
-## Usage (on Windows)
-- Make sure JDK version 8 or above is installed and JAVA_HOME environment variable is set
-- Use Powershell to execute the below commands
-- `PowerShell.exe -ExecutionPolicy UnRestricted -File .\script\setup.ps1` to download and extract portable sbt
-    - (If this script fails you can do this manually by visiting https://github.com/sbt/sbt/releases ,downloading the latest sbt zip and extracting it to ./coding-exercise-project/scala/sbt)
-- `.\sbt\sbt\bin\sbt test` to run tests
+- `./script/setup` to fetch dependencies
+- `./script/test` to run the tests, or `./script/test --watch` to re-run them on every change
+- `./script/start` to run the app
 
 ## Structure
 - Code located in [`Main.scala`](./src/main/scala/gu/com/Main.scala)

scala/script/setup

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
-set -e
+set -euo pipefail
 
-brew install --cask "guardian/devtools/gu-scala"
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+
+sbt update

scala/script/start

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+
+sbt run