Add local Debian package + plain binary build task

Adds packaging/local-build.sh and packaging/extract-binaries.sh, reused by a
new VS Code task, to populate gitignored dist/ and bin/ directories with the
same build.sh/test.sh/run.sh scripts the Gitea and GitHub workflows run.

packaging/local-build.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+# Populates repo-local dist/ (Debian packages) and bin/ (plain executables),
+# reusing the same scripts the Gitea and GitHub workflows run: build.sh and
+# test.sh directly when already inside the disposable packaging container
+# (e.g. this devcontainer), otherwise run.sh to build that container via Docker.
+set -euo pipefail
+root=$(cd -- "$(dirname -- "$0")/.." && pwd)
+dist="$root/dist"
+bindir="$root/bin"
+work=$(mktemp -d)
+trap 'rm -rf "$work"' EXIT
+if [[ -f /.dockerenv && $EUID == 0 ]]; then
+    apt-get update
+    bash "$root/packaging/build.sh" "$work"
+    bash "$root/packaging/test.sh" "$work"
+else
+    bash "$root/packaging/run.sh" "$work"
+fi
+rm -rf "$dist" "$bindir"
+mkdir -p "$dist" "$bindir"
+cp "$work"/* "$dist/"
+bash "$root/packaging/extract-binaries.sh" "$dist" "$bindir"
+echo "PASS: Debian packages in $dist, plain executables/libraries in $bindir"