fix(deps): dedupe packages mapped from multiple commands

The dependency map sends gcc/g++/make all to build-essential and
wrestool/icotool both to icoutils. The previous loop appended once
per missing command, so a clean machine printed:

  System dependencies needed:  p7zip-full wget icoutils icoutils
    imagemagick build-essential build-essential build-essential python3

apt dedupes internally so the install worked, but the log line read
as if the script was broken. Skip the append when the package is
already in deps_to_install; the bordered substring match handles
both build-essential and icoutils with a single rule.

Verified in a clean debian:stable-slim container with no build tools
present: build-essential and icoutils now appear exactly once in
each invocation.

Addresses review feedback on #401.

scripts/setup/dependencies.sh

@@ -48,20 +48,25 @@ check_dependencies() {
 		[make]='make' [python3]='python3'
 	)
 
-	local cmd
+	local cmd pkg
 	for cmd in $all_deps; do
 		if ! check_command "$cmd"; then
 			case "$distro_family" in
-				debian)
-					deps_to_install="$deps_to_install ${debian_pkgs[$cmd]}"
-					;;
-				rpm)
-					deps_to_install="$deps_to_install ${rpm_pkgs[$cmd]}"
-					;;
+				debian) pkg="${debian_pkgs[$cmd]}" ;;
+				rpm)    pkg="${rpm_pkgs[$cmd]}" ;;
 				*)
 					echo "Warning: Cannot auto-install '$cmd' on unknown distro. Please install manually." >&2
+					continue
 					;;
 			esac
+			# Several commands map to the same package (gcc/g++/make
+			# -> build-essential, wrestool/icotool -> icoutils). Skip
+			# if the package is already queued so the log line stays
+			# readable.
+			case " $deps_to_install " in
+				*" $pkg "*) ;;
+				*) deps_to_install="$deps_to_install $pkg" ;;
+			esac
 		fi
 	done