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/infrastructure/src/lib/adapters/graphql-issues.gateway.ts

@@ -25,6 +25,7 @@ import {
   BoardDocument,
   ChangeIssueStatusDocument,
   CreateIssueDocument,
+  DueIssuesDocument,
   EpicsDocument,
   IssueChildrenDocument,
   IssueDocument,
@@ -183,6 +184,14 @@ export class GraphqlIssuesGateway extends IssuesGateway {
     );
   }
 
+  due(projectId: string, from: string, to: string): Observable<IssueSummary[]> {
+    return this.gql
+      .query(DueIssuesDocument, {
+        filter: { projectId, dueFrom: from, dueTo: to },
+      })
+      .pipe(map((d) => d.issues.items.map(toIssueSummary)));
+  }
+
   trash(issueId: string): Observable<CommandResult> {
     return this.gql
       .mutate(TrashIssueDocument, { issueId })