feat: what is new since my last visit, and turning a comment into a ticket

Opening a ticket notes the visit and answers the one before (issue_visits),
so the page marks others' comments and changes since. A comment can become
a ticket of its own, as a subtask or linked; it remembers where it went.

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

libs/api/tracker/infrastructure/src/lib/mongo/read-model.schemas.ts

@@ -110,6 +110,7 @@ export const ReadModels = {
   AlertIntegration: 'AlertIntegration',
   AlertTrace: 'AlertTrace',
   TreeFollow: 'TreeFollow',
+  IssueVisit: 'IssueVisit',
   IssueReminder: 'IssueReminder',
   MyDay: 'MyDay',
   ReleaseNotesShare: 'ReleaseNotesShare',
@@ -373,6 +374,16 @@ export const TreeFollowSchema =
   SchemaFactory.createForClass(TreeFollowDocument);
 TreeFollowSchema.index({ userId: 1, issueId: 1 }, { unique: true });
 
+@Schema({ ...LOOSE, collection: 'issue_visits' })
+class IssueVisitDocument {
+  @Prop({ type: String }) userId!: string;
+  @Prop({ type: String }) issueId!: string;
+  @Prop({ type: String }) seenAt!: string;
+}
+export const IssueVisitSchema =
+  SchemaFactory.createForClass(IssueVisitDocument);
+IssueVisitSchema.index({ userId: 1, issueId: 1 }, { unique: true });
+
 @Schema({ ...LOOSE, collection: 'issue_reminders' })
 class IssueReminderDocument {
   @Prop({ type: String, required: true, unique: true }) id!: string;
@@ -511,6 +522,7 @@ export const READ_MODEL_SCHEMAS = [
   { name: ReadModels.AlertIntegration, schema: AlertIntegrationSchema },
   { name: ReadModels.AlertTrace, schema: AlertTraceSchema },
   { name: ReadModels.TreeFollow, schema: TreeFollowSchema },
+  { name: ReadModels.IssueVisit, schema: IssueVisitSchema },
   { name: ReadModels.IssueReminder, schema: IssueReminderSchema },
   { name: ReadModels.MyDay, schema: MyDaySchema },
   { name: ReadModels.ReleaseNotesShare, schema: ReleaseNotesShareSchema },