feat: due-date reminders

Every hour the API reminds whoever has a ticket, and whoever follows it,
the day before its due date, on the day and once when it is overdue, in
the app and by e-mail for those who asked. Cards on the board flag what
is due soon or late.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/domain/src/index.ts

@@ -10,3 +10,4 @@ export * from './lib/models/estimation';
 export * from './lib/models/swimlanes';
 export * from './lib/models/roadmap';
 export * from './lib/models/shortcuts';
+export * from './lib/models/due';