!explain via ❓ reaction: thread-reply with a 3-bullet TL;DR

When a user reacts ❓ on one of Pete's posts, fetch the article body,
ask Ollama for a 3-bullet summary, and post it as a threaded reply
rooted at the original story event. Per-process cooldown of 5min per
story keeps repeated reactions from re-summarizing.

- ingestion.FetchArticleBody: visible <p> text capped at 8000 chars
- classifier.OllamaClient.GenerateText: non-JSON variant
- storage.GetStoryByGUID: full row lookup
- matrix.PostThreadedReply: m.thread + m.in_reply_to fallback
- poster.SetReactionCallback: optional hook fired after recording
- New package: internal/explainer

internal/storage/queries.go

@@ -118,6 +118,18 @@ func GetUnclassifiedStories(source string) ([]Story, error) {
 	return stories, rows.Err()
 }
 
+// GetStoryByGUID returns the full story record for a GUID, or nil if not found.
+func GetStoryByGUID(guid string) (*Story, error) {
+	row := Get().QueryRow(
+		`SELECT guid, headline, lede, image_url, article_url, source, feed_hint, platforms, channel, seen_at
+		 FROM stories WHERE guid = ?`, guid)
+	var s Story
+	if err := row.Scan(&s.GUID, &s.Headline, &s.Lede, &s.ImageURL, &s.ArticleURL, &s.Source, &s.FeedHint, &s.Platforms, &s.Channel, &s.SeenAt); err != nil {
+		return nil, err
+	}
+	return &s, nil
+}
+
 // InsertRecentHeadline adds a headline to the dedup context window.
 func InsertRecentHeadline(guid, headline, source string) {
 	exec("insert recent_headline",