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/infrastructure/src/lib/mongo/find.repositories.ts

@@ -166,6 +166,7 @@ export class MongoFindIssuesRepository extends FindIssuesRepository {
       trashedAt: null,
     };
     if (filter.assigneeId) query['assignee.id'] = filter.assigneeId;
+    if (filter.watcherId) query['watchers.id'] = filter.watcherId;
     if (filter.statuses?.length) query['status'] = { $in: filter.statuses };
     if (filter.categories?.length)
       query['statusCategory'] = { $in: filter.categories };
@@ -431,6 +432,7 @@ function toMongoFilter(filter: IssueFilter): FilterQuery<IssueDoc> {
   else if (filter.sprintId) query['sprint.id'] = filter.sprintId;
   if (filter.unassigned) query['assignee'] = null;
   else if (filter.assigneeId) query['assignee.id'] = filter.assigneeId;
+  if (filter.watcherId) query['watchers.id'] = filter.watcherId;
   if (filter.search?.trim()) {
     const pattern = new RegExp(escapeRegex(filter.search.trim()), 'i');
     query.$or = [