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>

apps/api/schema.gql

@@ -508,6 +508,9 @@ input IssueFilterInput {
   statuses: [String!]
   types: [String!]
   unassigned: Boolean
+
+  """Only the tickets I follow (none when anonymous)"""
+  watching: Boolean
 }
 
 type IssueLink {
@@ -960,6 +963,9 @@ type Query {
     """Matches key, title or description (global search)"""
     search: String
     statuses: [String!]
+
+    """Only the tickets I follow"""
+    watching: Boolean! = false
   ): IssuePage!
 
   """My notifications, newest first, and how many are unread"""