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/application/src/lib/ports/find-issues.repository.ts

@@ -28,6 +28,9 @@ export interface IssueFilter {
   /** Only the tickets hanging from this one. */
   parentId?: string;
   sprintId?: string;
+  /** Due between these days (`YYYY-MM-DD`, both included). */
+  dueFrom?: string;
+  dueTo?: string;
   /** Only tickets in no sprint (wins over `sprintId`). */
   noSprint?: boolean;
   /** RECENT (default): last updated first. RANK: backlog order. */