Fix Decline NPE, add //> using files directive to auto-include src/

[Copilot]

Two bugs: a runtime NullPointerException crashing every build/serve/verify invocation, and src/ having to be passed explicitly on every Scala CLI command.

Runtime NullPointerException in Build

Classic Scala object init-order bug. command was declared first but referenced buildCmd/serveCmd/verifyCmd — all still null at that point. Decline stored the nulls and blew up during argument parsing:

NullPointerException: Cannot invoke "com.monovore.decline.Command.name()" because "command" is null
    at com.monovore.decline.Help$.collectCommandHelp(Help.scala:286)

Fixed by moving the three sub-command vals above command in src/Build.scala.

Auto-include src/ via directive

Added //> using files "./src/" to build.scala so the source directory is baked into the build descriptor. Cleaned up the now-redundant explicit src/ argument from:

• Makefile — scala-compile and scala-build targets
• .github/workflows/build.yml — both compile and run steps

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• central.sonatype.com
  • Triggering command: /home/REDACTED/.cache/coursier/v1/https/github.com/VirtusLab/scala-cli/releases/download/v1.12.4/scala-cli-x86_64-pc-linux /home/REDACTED/.cache/coursier/v1/https/github.com/VirtusLab/scala-cli/releases/download/v1.12.4/scala-cli-x86_64-pc-linux compile ./build.scala (dns block)
• repo.scala-lang.org
  • Triggering command: /home/REDACTED/.cache/coursier/v1/https/github.com/VirtusLab/scala-cli/releases/download/v1.12.4/scala-cli-x86_64-pc-linux /home/REDACTED/.cache/coursier/v1/https/github.com/VirtusLab/scala-cli/releases/download/v1.12.4/scala-cli-x86_64-pc-linux compile ./build.scala (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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