feat: conversations on a ticket are settled, and you see who is typing

A top-level comment and its replies can be resolved by whoever can
change the ticket (CommentThreadResolvedEvent), with an optional
conclusion added as a reply marked as a decision, so it shows above the
ticket. A settled conversation folds to one line (topic, who settled it
and the conclusion) and can be unfolded or reopened; the header counts
the open ones, and finishing the ticket with one open asks first.

«Ana está escribiendo…» shows in the conversation being answered, at
once: a `typing` mutation publishes to a Redis channel per ticket
(`typing` subscription), never stored. In replies, Enter sends and
Shift+Enter breaks the line, except inside lists and code.

API: resolveThread / PUT-DELETE /api/comments/{id}/resolution, Comment
.resolved/resolvedBy/resolvedAt, typing mutation and subscription. MCP:
resolve_thread.

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

libs/api/tracker/domain/src/lib/comment/comment.ts

@@ -6,6 +6,7 @@ import {
 } from '@task-stream/api/shared/domain';
 import { CommentAddedEvent } from '../events/comment-added.event';
 import { CommentDecisionMarkedEvent } from '../events/comment-decision-marked.event';
+import { CommentThreadResolvedEvent } from '../events/comment-thread-resolved.event';
 import { CommentDeletedEvent } from '../events/comment-deleted.event';
 import { CommentEditedEvent } from '../events/comment-edited.event';
 import { CommentReactedEvent } from '../events/comment-reacted.event';
@@ -44,6 +45,8 @@ export class Comment extends VersionedAggregateRoot implements CommentProps {
   public reactions: Record<string, string[]> = {};
   /** What was decided on the ticket: shown above it and searchable. */
   public decision = false;
+  /** A top-level comment whose conversation was settled. */
+  public resolved = false;
   public deleted = false;
   public createdAt!: string;
   public editedAt: string | null = null;
@@ -114,6 +117,28 @@ export class Comment extends VersionedAggregateRoot implements CommentProps {
     );
   }
 
+  /**
+   * Settles the conversation this comment opens (`on`) or reopens it;
+   * repeating it changes nothing. Only a top-level comment opens one.
+   */
+  resolveThread(actorId: string, on: boolean): void {
+    this.assertAlive();
+    if (this.replyTo)
+      throw new BusinessRuleError(
+        'Only a conversation is resolved, not a reply',
+      );
+    if (on === this.resolved) return;
+    this.apply(
+      new CommentThreadResolvedEvent(
+        actorId,
+        this.id,
+        this.projectId,
+        this.issueId,
+        on,
+      ),
+    );
+  }
+
   /** @param canModerate whether the actor manages the project (may delete others' comments). */
   delete(actorId: string, canModerate: boolean): void {
     this.assertAlive();
@@ -146,6 +171,10 @@ export class Comment extends VersionedAggregateRoot implements CommentProps {
     this.decision = event.decision;
   }
 
+  onCommentThreadResolvedEvent(event: CommentThreadResolvedEvent): void {
+    this.resolved = event.resolved;
+  }
+
   onCommentDeletedEvent(): void {
     this.deleted = true;
   }