Images phase 1: attention-triggered og:image coverage

Tie image enrichment to attention (per review): when an article earns a summary
(i.e. a reader reached it), best-effort fetch a real og:image if it lacks one —
never blanket-fetch every ingested article. Adds:

* enrich_article_image() — single-article fetch, leaves existing images alone,
  retries an imageless article only after 7 days, stamps image_checked_at.
* generate_summary() calls it after caching (wrapped; never breaks summaries).
* enrich_summarized_images() + `goodnews enrich-images` CLI — slow background
  backfill of already-summarized, accepted, imageless articles.
* Quality gate: extend the generic-image skip list with data:/tracking-pixel/
  spacer markers (on top of the existing logo/placeholder + unbranded-BBC logic).

This is coverage only; display (editorial rhythm, tile treatment) comes next.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

goodnews/summarize.py

@@ -104,4 +104,12 @@ def generate_summary(conn: sqlite3.Connection, article_id: int, client: LocalMod
         (article_id, summary, client.model),
     )
     conn.commit()
+    # Attention-triggered image enrichment: a summarized article is one a reader
+    # has reached, so it's worth a real image. Best-effort — an image fetch
+    # failure must never break summarization.
+    try:
+        from .enrich import enrich_article_image
+        enrich_article_image(conn, article_id)
+    except Exception:
+        pass
     return summary