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/api/tracker/infrastructure/src/lib/mongo/find.repositories.ts

@@ -238,6 +238,18 @@ export class MongoFindIssuesRepository extends FindIssuesRepository {
     return docs.map(issueFromDoc);
   }
 
+  async findDueBy(day: string): Promise<IssueReadModel[]> {
+    const docs = await this.issues
+      .find({
+        dueDate: { $ne: null, $lte: `${day}\uffff` },
+        statusCategory: { $nin: FINISHED },
+        $or: [{ assignee: { $ne: null } }, { 'watchers.0': { $exists: true } }],
+      })
+      .limit(5000)
+      .lean<IssueDoc[]>();
+    return docs.map(issueFromDoc);
+  }
+
   async findByProject(projectId: string): Promise<IssueReadModel[]> {
     const docs = await this.issues.find({ projectId }).lean<IssueDoc[]>();
     return docs.map(issueFromDoc);