feat: a calendar to subscribe to, and the backlog's corners

- Each person can subscribe their dates in Google Calendar, Outlook or
  Apple Calendar: GET /api/calendar/{token}.ics (no session) brings
  their unfinished tickets with a due date (assigned or followed), the
  planned and running sprints and the planned releases of their
  projects, as all-day events linking to the web. The token is made,
  renewed or dropped under /me/calendar (and in GraphQL); in the web,
  from «Calendario» in «Mi trabajo».
- The backlog panel keeps the selected rows' background inside its
  rounded corners.

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

libs/api/tracker/application/src/index.ts

@@ -19,6 +19,8 @@ export * from './lib/git.service';
 export * from './lib/webhooks.service';
 export * from './lib/transfer.service';
 export * from './lib/automations.service';
+export * from './lib/calendar.service';
+export * from './lib/calendar/calendar';
 export * from './lib/automations/automations';
 export * from './lib/automations/automation-rules';
 export * from './lib/transfer/import-export';