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/infrastructure/src/lib/tracker-infrastructure.providers.ts

@@ -9,6 +9,7 @@ import {
   CommentsGateway,
   IssuesGateway,
   NotificationsGateway,
+  CalendarGateway,
   ProjectsGateway,
   ReleasesGateway,
   SavedFiltersGateway,
@@ -28,6 +29,7 @@ import {
 } from './adapters/graphql-collaboration.gateways';
 import { GraphqlIssuesGateway } from './adapters/graphql-issues.gateway';
 import { GraphqlNotificationsGateway } from './adapters/graphql-notifications.gateway';
+import { GraphqlCalendarGateway } from './adapters/graphql-calendar.gateway';
 import { HttpAttachmentsGateway } from './adapters/http-attachments.gateway';
 import { HttpProposalsGateway } from './adapters/http-proposals.gateway';
 import { GraphqlProjectsGateway } from './adapters/graphql-projects.gateway';
@@ -51,6 +53,7 @@ export function provideTrackerInfrastructure(): EnvironmentProviders {
     { provide: ProposalsGateway, useClass: HttpProposalsGateway },
     { provide: UsersGateway, useClass: GraphqlUsersGateway },
     { provide: NotificationsGateway, useClass: GraphqlNotificationsGateway },
+    { provide: CalendarGateway, useClass: GraphqlCalendarGateway },
     { provide: TrackerRealtimeGateway, useClass: GraphqlRealtimeGateway },
     { provide: SavedFiltersGateway, useClass: GraphqlSavedFiltersGateway },
     { provide: SprintsGateway, useClass: GraphqlSprintsGateway },