feat: a sprint calendar

A Calendario tab lays the project's sprints out month by month as bands,
with the releases and the tickets due on each day. Owners and admins plan
a sprint by clicking the day it starts, and the whole plan downloads as an
iCalendar file. Tickets can be searched by due-date range.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/app/app.routes.spec.ts

@@ -30,6 +30,7 @@ describe('appRoutes', () => {
       'issues/:issueKey',
       'backlog',
       'sprints',
+      'calendar',
       'roadmap',
       'epics',
       'trash',