!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/ingestion/article.go

@@ -101,6 +101,69 @@ func FetchOGImage(articleURL string) string {
 	return FetchArticleMeta(articleURL).ImageURL
 }
 
+// MaxBodyChars is the cap on body text returned by FetchArticleBody. Keeps
+// LLM prompts bounded; most news articles fit well under this.
+const MaxBodyChars = 8000
+
+// FetchArticleBody fetches the article and returns the concatenated visible
+// body text (<article>/<main> <p> tags, falling back to all <p>), trimmed
+// and capped at MaxBodyChars. Returns "" on any fetch failure.
+func FetchArticleBody(articleURL string) string {
+	if articleURL == "" {
+		return ""
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 12*time.Second)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(ctx, "GET", articleURL, nil)
+	if err != nil {
+		return ""
+	}
+	req.Header.Set("User-Agent", userAgent)
+	req.Header.Set("Accept", "text/html,application/xhtml+xml")
+
+	resp, err := articleClient.Do(req)
+	if err != nil {
+		return ""
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return ""
+	}
+
+	doc, err := goquery.NewDocumentFromReader(resp.Body)
+	if err != nil {
+		return ""
+	}
+	return extractBodyText(doc)
+}
+
+func extractBodyText(doc *goquery.Document) string {
+	sel := doc.Find("article p, main p")
+	if sel.Length() == 0 {
+		sel = doc.Find("p")
+	}
+	var b strings.Builder
+	sel.Each(func(_ int, s *goquery.Selection) {
+		t := strings.TrimSpace(s.Text())
+		if t == "" {
+			return
+		}
+		if b.Len() > 0 {
+			b.WriteString("\n\n")
+		}
+		b.WriteString(t)
+		if b.Len() >= MaxBodyChars {
+			return
+		}
+	})
+	out := strings.TrimSpace(b.String())
+	if len(out) > MaxBodyChars {
+		out = out[:MaxBodyChars]
+	}
+	return out
+}
+
 func extractOGImage(doc *goquery.Document, base string) string {
 	selectors := []string{
 		`meta[property="og:image:secure_url"]`,