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>

apps/api/schema.gql

@@ -705,6 +705,9 @@ type Issue {
   """Linked tickets I can see"""
   linkedIssues: [Issue!]!
   links: [IssueLink!]!
+
+  """My waiting reminder on it (null without one or a token)"""
+  myReminder: IssueReminder
   number: Int!
 
   """The epic or ticket this one breaks down"""
@@ -845,6 +848,13 @@ enum IssuePriority {
   MEDIUM
 }
 
+"""My own reminder on a ticket («remind me on Thursday»)"""
+type IssueReminder {
+  """When it tells me (ISO, UTC)"""
+  at: String!
+  note: String
+}
+
 """RECENT: last updated first. RANK: backlog order."""
 enum IssueSort {
   RANK
@@ -971,6 +981,9 @@ type Mutation {
   changeIssueStatus(input: ChangeIssueStatusInput!): CommandResult!
   changeProjectMemberRole(input: ProjectMemberInput!): CommandResult!
 
+  """Drop my reminder on a ticket"""
+  clearReminder(issueId: ID!): Boolean!
+
   """
   Close the sprint under way. Unfinished tickets move to carryOverToSprintId, or back to the backlog when it is null.
   """
@@ -1103,6 +1116,16 @@ type Mutation {
   """Put a ticket in a sprint (null: back to the backlog)"""
   setIssueSprint(issueId: ID!, sprintId: ID): CommandResult!
 
+  """
+  Remind me of a ticket at a date and time (a notification), with an optional note. One per ticket: it replaces the waiting one
+  """
+  setReminder(
+    """ISO date-time, in the future"""
+    at: String!
+    issueId: ID!
+    note: String
+  ): IssueReminder!
+
   """Turn the link on or change its blocks; renew for a new secret"""
   shareDashboard(input: ShareDashboardInput!): DashboardShare!
 
@@ -1645,6 +1668,9 @@ type Query {
   """Projects where I am a member"""
   myProjects: [Project!]!
 
+  """My waiting reminders on tickets, soonest first"""
+  myReminders: [ReminderOnIssue!]!
+
   """My saved views of my work, across my projects"""
   myViews: [MyView!]!
   notificationSettings: NotificationSettings!
@@ -1779,6 +1805,12 @@ enum ReleaseStatus {
   RELEASED
 }
 
+"""One of my waiting reminders, with its ticket"""
+type ReminderOnIssue {
+  issue: Issue!
+  reminder: IssueReminder!
+}
+
 """Tickets to look at now (worst first)"""
 type Risks {
   blocked: [InsightIssue!]!