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/presenters/src/lib/http/dto/responses.dto.ts

@@ -831,6 +831,15 @@ export class MyNotificationsDto {
   unread!: number;
 }
 
+export class CalendarFeedDto {
+  @ApiProperty({
+    description:
+      'Secret of the calendar URL: GET /api/calendar/{token}.ics (iCalendar, no session)',
+  })
+  token!: string;
+  @ApiProperty() createdAt!: string;
+}
+
 export class NotificationSettingsResponseDto {
   @ApiProperty({ description: 'Copies by e-mail' }) email!: boolean;
   @ApiProperty({ description: 'Whether this installation can send e-mail' })