Fix !post in round-robin mode, ❓ reaction VS16, image label

- !post falls back to newest unposted story for the channel when the
  in-memory queue is empty (the steady state under round-robin).
- Accept ❓️/❔️ (U+FE0F variation selector) as question reactions —
  the bare codepoints alone missed clients that render the colored emoji.
- Rewrite Guardian i.guim.co.uk thumbnails to width=1200 so we stop
  rejecting real images as "tracking pixels"; relabel the size warning.
- Log decrypt failures and reactions on events not in post_log so future
  silent drops surface instead of vanishing.

main.go

@@ -92,11 +92,35 @@ func main() {
 		if queue.ForcePost(channel) {
 			return
 		}
+		// In-memory queue empty (common in round-robin mode). Fall back to the
+		// newest classified, not-yet-posted story for this channel.
+		story, err := storage.GetNewestPostableStoryByChannel(channel)
+		if err != nil {
+			slog.Error("!post: db lookup failed", "channel", channel, "err", err)
+			return
+		}
+		if story != nil {
+			imageURL := ""
+			if story.ImageURL != "" && ingestion.ValidateImageURL(story.ImageURL) {
+				imageURL = story.ImageURL
+			}
+			queue.PostNow(poster.QueueItem{
+				GUID:       story.GUID,
+				Headline:   story.Headline,
+				Lede:       story.Lede,
+				ImageURL:   imageURL,
+				ArticleURL: story.ArticleURL,
+				Source:     story.Source,
+				Channel:    story.Channel,
+				Platforms:  storage.UnmarshalPlatforms(story.Platforms),
+			})
+			return
+		}
 		if err := mx.PostThreadedReply(channel, eventID,
-			"nothing queued for "+channel,
-			"nothing queued for <code>"+channel+"</code>",
+			"nothing available for "+channel,
+			"nothing available for <code>"+channel+"</code>",
 		); err != nil {
-			slog.Warn("!post: failed to send empty-queue reply", "err", err)
+			slog.Warn("!post: failed to send empty reply", "err", err)
 		}
 	})