feat: «Recordármelo», a reminder of a ticket only for me

On a ticket, «Recordármelo» offers in an hour, this evening, tomorrow or
next Monday at 9, in a week, or any date and time, with an optional note.
The ticket shows the waiting one («Te lo recordaré el mié 21 a las 9:00»)
to change or drop. Every minute a scheduler tells the ones whose time
came as a REMINDER notification (bell, push, e-mail), once, and forgets
those whose ticket went to the trash or out of reach. One per person and
ticket, private, no history (Mongo `issue_reminders`).

API: setReminder / clearReminder, Issue.myReminder, myReminders;
PUT/DELETE /api/issues/{issue}/reminder, GET /api/me/reminders. MCP:
remind_me.

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

libs/web/tracker/domain/src/lib/ports/gateways.ts

@@ -150,6 +150,13 @@ export abstract class IssuesGateway {
   abstract pin(issueId: string, pinned: boolean): Observable<void>;
   /** Follows the ticket with everything under it (or stops). */
   abstract followTree(issueId: string, on: boolean): Observable<void>;
+  /** Reminds me of the ticket then (replaces the waiting one). */
+  abstract setReminder(
+    issueId: string,
+    at: string,
+    note: string | null,
+  ): Observable<void>;
+  abstract clearReminder(issueId: string): Observable<void>;
   /**
    * Decisions (comments marked as such) of all my projects by their text,
    * most recent first: here and not in CommentsGateway, for the palette.