Refactor time tracker UI (#34983)

Although we decided to "reduce the button amount" on the side bar, not
only one user reported that the "time tracker dropdown" is not easy to
use.

So the best we can do at the moment is: move the buttons to the sidebar
again.

Fix #34979

web_src/css/modules/button.css

@@ -366,8 +366,8 @@ It needs some tricks to tweak the left/right borders with active state */
 
 .ui.buttons .button {
   border-right: none;
-  flex: 1 0 auto;
   border-radius: 0;
+  flex-shrink: 0;
   margin: 0;
 }
 .ui.buttons .button:first-child {