Document include=assets as the way to see a ticket's associated assets

The /tickets/{id}/associated-assets path 404s on this instance; assets come
back embedded via GET /tickets/{id}?include=assets. Spell out the full include
list on get_ticket and in the skill reference so consumers don't hunt for a
nonexistent endpoint.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

reference.md

@@ -86,6 +86,11 @@ lists which ones they're in).
 - `GET /tickets` supports `filter` presets (`new_and_my_open`, `watching`,
   `spam`, `deleted`), `updated_since`, `order_by`, `order_type`, `page`,
   `per_page` (max 100), and `include` (`conversations`, `requester`, `stats`).
+- `GET /tickets/{id}?include=assets` is the **only** way to see a ticket's
+  associated CMDB assets — they come back embedded in the ticket object. There
+  is no `/tickets/{id}/associated-assets` endpoint (it 404s). Other
+  single-ticket includes: `conversations`, `requester`, `requested_for`,
+  `stats`, `problem`, `tags`, `related_tickets`.
 - `GET /tickets/filter?query="..."` is for ad-hoc field queries (also 100/page).
 
 ## Pagination & rate limits