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/create-nvim-keymaps.sh

@@ -28,6 +28,7 @@ main()
     && mv "${DEST}.tmp" "$DEST"
 
   msg "Neovim keybindings documentation generated at $DEST"
+  return 0
 }
 
 main "$@"