Add a year view to the calendar

Pull in @fullcalendar/multimonth so the deadline calendar can show all
twelve months at once, between the month grid and the year list. Events
render as dots there and the type scales down, so the month tables stay
legible two or three to a row.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

site/package.json

@@ -6,6 +6,7 @@
   "dependencies": {
     "@fullcalendar/core": "^6.1.15",
     "@fullcalendar/daygrid": "^6.1.15",
-    "@fullcalendar/list": "^6.1.15"
+    "@fullcalendar/list": "^6.1.15",
+    "@fullcalendar/multimonth": "^6.1.21"
   }
 }