fix(shell): add explicit return statements to functions

Add return 0 as the last statement in ~46 shell functions across
17 files that previously relied on implicit return codes
(SonarCloud rule shelldre:S7682).

scripts/install-z.sh

@@ -20,12 +20,14 @@ clone_z_repo()
   else
     msgr ok "z ($bin_path/) already installed"
   fi
+  return 0
 }
 
 # Main function
 main()
 {
   clone_z_repo "$Z_GIT_PATH" "$Z_BIN_PATH"
+  return 0
 }
 
 main "$@"