feat: tickets I follow, and more news for followers

"Que sigo" on the home page lists the open tickets I follow, whoever
works on them; `watching` filters my issues (REST, GraphQL, MCP) and a
project's search (none without a session).

Followers now also hear when a ticket's priority or due date changes,
and when it enters or leaves a sprint. Smaller edits (title, labels…)
still do not notify.

Docs (with the REPLIED row the replies change missed), Word and PDF
updated.

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

libs/api/tracker/application/src/lib/queries/search-issues.query-handler.ts

@@ -15,8 +15,12 @@ export class SearchIssuesQueryHandler
 
   async execute(query: SearchIssuesQuery): Promise<Page<IssueReadModel>> {
     await this.access.assertCanView(query.filter.projectId, query.viewerId);
+    const { watching, ...filter } = query.filter;
+    // Someone anonymous follows nothing.
+    if (watching && !query.viewerId) return { items: [], total: 0 };
     return this.findIssues.search({
-      ...query.filter,
+      ...filter,
+      watcherId: watching ? (query.viewerId ?? undefined) : undefined,
       limit: Math.min(query.filter.limit, 200),
     });
   }