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/web/tracker/presenters/src/lib/pages/backlog.page.ts

@@ -178,6 +178,8 @@ import { initials, PRIORITY, statusLook, typeLook } from '../ui/copy';
       margin: 0;
       padding: 0.25rem 0;
       list-style: none;
+      /* Selected rows have a background: kept inside the rounded corners. */
+      overflow: hidden;
     }
     .ts-backlog__row {
       display: grid;