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/api/tracker/presenters/src/lib/graphql/inputs.ts

@@ -508,6 +508,20 @@ export class IssueFilterInput {
   @IsOptional()
   @IsBoolean()
   noSprint?: boolean;
+  @Field({
+    nullable: true,
+    description: 'Due on or after this day (YYYY-MM-DD)',
+  })
+  @IsOptional()
+  @Matches(/^\d{4}-\d{2}-\d{2}$/)
+  dueFrom?: string;
+  @Field({
+    nullable: true,
+    description: 'Due on or before this day (YYYY-MM-DD)',
+  })
+  @IsOptional()
+  @Matches(/^\d{4}-\d{2}-\d{2}$/)
+  dueTo?: string;
   @Field(() => IssueSort, { nullable: true, defaultValue: IssueSort.RECENT })
   @IsOptional()
   @IsEnum(IssueSort)