Floor the calendar height so a short window cannot squash it

The viewport-relative height can resolve smaller than the grid needs on a short
window - a laptop with a docked browser, or a display in portrait - which would
have reintroduced the squashing it was meant to fix. Three floors now: the
container, the calendar root, and each day cell.

The day cell is the one that matters: six week rows cannot render shorter than
about 660px however short the window, so the grid stays readable rather than
collapsing back to strips.

plugins/notifications/frontend/views/CalendarView.vue

@@ -265,6 +265,13 @@ function formatDate(dateStr) {
   min-height: 110px;
 }
 
+/* The calc() height above is viewport-relative, so on a short window - a laptop
+   with a docked browser, or a shopfloor display in portrait - it can resolve
+   smaller than the grid needs. This stops it undercutting the day cells. */
+:deep(.fc) {
+  min-height: 620px;
+}
+
 /* The day number was tight against the top edge once the cells grew. */
 :deep(.fc-daygrid-day-top) {
   padding: 2px 4px;