feat: replies to comments

A comment can answer another one (replyTo), one level deep: answering a
reply joins the same thread, and it must be on the same ticket. Whoever
wrote the comment gets a new REPLIED notification, and the activity says
"respondió a un comentario".

A comment deleted while it has replies stays, without its text
(deleted: true), so the thread still reads; it goes with its last reply
and does not count in commentCount.

The ticket page shows threads with their replies indented and a
"Responder" box; REST, GraphQL and the MCP (add_comment, get_issue) take
and show replyTo. Existing comments are unchanged. Docs, Word and PDF
updated.

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

libs/web/tracker/application/src/lib/events/issue.events.ts

@@ -39,6 +39,8 @@ export const issuePageEvents = eventGroup({
       body: string;
       /** Uploaded under the new comment once it exists. */
       files?: File[];
+      /** Comment it answers (one level of replies). */
+      replyTo?: string | null;
     }>(),
     watchRequested: type<{ issueId: string; watching: boolean }>(),
     trashRequested: type<{ issueId: string; trashed: boolean }>(),

libs/web/tracker/application/src/lib/facades/issue.facade.ts

@@ -92,10 +92,14 @@ export class IssueFacade {
     );
   }
 
-  /** `files` are attached under the new comment. */
-  addComment(body: string, files: File[] = []): void {
+  /** `files` are attached under the new comment; `replyTo` answers one. */
+  addComment(
+    body: string,
+    files: File[] = [],
+    replyTo: string | null = null,
+  ): void {
     this.withIssue((issueId) =>
-      this.dispatch.commentAddRequested({ issueId, body, files }),
+      this.dispatch.commentAddRequested({ issueId, body, files, replyTo }),
     );
   }
 

libs/web/tracker/application/src/lib/stores/issue.store.ts

@@ -460,7 +460,7 @@ export const IssueStore = signalStore(
               mergeMap(({ payload }) =>
                 runCommand(
                   comments
-                    .add(payload.issueId, payload.body)
+                    .add(payload.issueId, payload.body, payload.replyTo ?? null)
                     .pipe(
                       concatMap((comment) =>
                         payload.files?.length
@@ -474,7 +474,9 @@ export const IssueStore = signalStore(
                     ),
                   payload.files?.length
                     ? 'Comentario y adjuntos añadidos'
-                    : 'Comentario añadido',
+                    : payload.replyTo
+                      ? 'Respuesta añadida'
+                      : 'Comentario añadido',
                   done,
                   failed,
                 ),