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>

libs/web/tracker/domain/src/index.ts

@@ -11,3 +11,4 @@ export * from './lib/models/swimlanes';
 export * from './lib/models/roadmap';
 export * from './lib/models/shortcuts';
 export * from './lib/models/due';
+export * from './lib/models/calendar';