Web page designer ProgressBar preview animates, overflows its selection rectangle, and ignores the app theme

The Web page designer's ProgressBar preview did not match the running Web app. The designer animated indeterminate ProgressBars (the desktop designer intentionally shows them static), the drawn bar could spill outside the control's selection rectangle, and the preview used the Studio theme instead of the app's Web theme, so it looked nothing like the ProgressBar in the browser. The page designer now draws the ProgressBar exactly like the browser does: a themed track with an accent fill, using the app's theme tokens, with indeterminate controls shown as a static half-filled bar and every element kept inside the selection rectangle.