fix(diagrams): replace par/and/end with group in seq-polling

par keyword is not supported in the PlantUML version on the Gitea runner.
Replace with a group block (universally supported) and a spanning note
to convey the parallelism.

docs/diagrams/seq-polling.puml

@@ -35,33 +35,28 @@ config --> poller : [{ id, url, apiKey }]
 poller -> config : getRadarrInstances()
 config --> poller : [{ id, url, apiKey }]
 
-note over poller : All fetches run in\nparallel via Promise.all,\neach wrapped in timed()
+note over poller, cache
+  All 9 fetches run in parallel via Promise.all,
+  each wrapped in timed(). Shown sequentially below.
+end note
 
-par SABnzbd Queue
+group Parallel API Fetches (Promise.all)
   poller -> sab : GET /api?mode=queue
   sab --> poller : { queue: { slots, status, speed } }
-and SABnzbd History
   poller -> sab : GET /api?mode=history&limit=10
   sab --> poller : { history: { slots } }
-and Sonarr Tags
   poller -> sonarr : GET /api/v3/tag
   sonarr --> poller : [{ id, label }]
-and Sonarr Queue
-  poller -> sonarr : GET /api/v3/queue\n?includeSeries=true
+  poller -> sonarr : GET /api/v3/queue?includeSeries=true
   sonarr --> poller : { records: [{ seriesId, series, ... }] }
-and Sonarr History
-  poller -> sonarr : GET /api/v3/history\n?pageSize=10
+  poller -> sonarr : GET /api/v3/history?pageSize=10
   sonarr --> poller : { records: [{ seriesId, ... }] }
-and Radarr Queue
-  poller -> radarr : GET /api/v3/queue\n?includeMovie=true
+  poller -> radarr : GET /api/v3/queue?includeMovie=true
   radarr --> poller : { records: [{ movieId, movie, ... }] }
-and Radarr History
-  poller -> radarr : GET /api/v3/history\n?pageSize=10
+  poller -> radarr : GET /api/v3/history?pageSize=10
   radarr --> poller : { records: [{ movieId, ... }] }
-and Radarr Tags
   poller -> radarr : GET /api/v3/tag
   radarr --> poller : [{ id, label }]
-and qBittorrent
   poller -> qbt : getTorrents()
   qbt --> poller : [{ name, progress, ... }]
 end