ots page: fix zero horizontal margin on mobile

`.ots-calendars { padding: 1rem 0 }` zeroed Bootstrap's responsive
horizontal padding on the parent .container-xl, so on small screens
the page content sat flush against the viewport edge (the
screenshot showed text touching the left side at 0px).

Split into explicit padding-top + padding-bottom so the container's
--bs-gutter-x stays intact and we still get vertical breathing room.

Author: hans-crypto

frontend/src/app/components/_ordpool/open-timestamps/open-timestamps.component.scss

@@ -1,5 +1,10 @@
 .ots-calendars {
-  padding: 1rem 0;
+  // Vertical breathing room only -- leave Bootstrap's responsive
+  // horizontal padding (--bs-gutter-x on .container-xl) intact.
+  // Setting `padding: 1rem 0` here zeroes the horizontal padding and
+  // the page content slams against the viewport edge on mobile.
+  padding-top: 1rem;
+  padding-bottom: 1rem;
 
   .text-right {
     text-align: right;