This feature already exists since a couple of versions:

By mistake. Thanks for the reminder.

That can be changed by the user (see blog). If you have found a clearly better alternative, you are welcome to share it.

If you switch to light theme, it already should show tags more noticeable.

We suggest to (also) ask the Git community to improve the handling, e.g., using auto-stash.

Thanks for the explanation.

Do you want to get a feature to stage all committable files or all visible committable files? The difference between becomes obvious, if you have selected just a directory (instead of the repository root) or filtered the file list by name.

Do you need a toolbar button or would be a menu item with keyboard shortcut be sufficient?

Please describe your full workflow so I understand why you need it. In other Git clients you need it, because they can't commit without staging. In SmartGit, however, you can commit without staging first.

If you want to stage all files to commit all files, forget the stage and commit. You will be asked whether to commit the selected file or all files.

As stated above, this feature is implemented in version 23.1.

SmartGit 23.1 build 20112 will contain the low-level property 

styledtext.useOwnWordBoundaryDetection to disable our changes and use the system default.