Durable image quality: stop trusting feed thumbnails; cycle enriches Latest

Make "no blurry images" sustainable, not a one-off cleanup. RSS feed thumbnails
(~44% were ~90px) were stored at ingest and upscaled to mush, so new articles
would reintroduce them. Now image_url is filled ONLY by the quality-gated
og:image enrichment:

* insert_article no longer stores the feed image (was canonicalize_url(item...)).
* enrich_recent_images(): the cycle fetches a quality og:image for the newest
  accepted, imageless articles each run (bounded), keeping Latest photo-rich.
* Brief + on-open enrichment unchanged.

Net: every stored image is a validated, ≥450px og:image; the rest are clean
placeholders.

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

tests/test_enrich_images.py

@@ -78,3 +78,19 @@ def test_image_dimensions_parses_headers():
     gif = b"GIF89a" + struct.pack("<HH", 90, 90)
     assert enrich._image_dimensions(gif) == (90, 90)
     assert enrich._image_dimensions(b"not an image at all") is None
+
+
+def test_enrich_recent_targets_newest_imageless_accepted(tmp_path):
+    c = _setup(tmp_path)
+    # newest first by published_at; summary not required (unlike the backfill)
+    c.execute("INSERT INTO articles (id,source_id,canonical_url,title,url_hash,image_url,published_at) "
+              "VALUES (1,1,'u1','T1','h1',NULL,'2026-01-01T00:00:00')")
+    c.execute("INSERT INTO articles (id,source_id,canonical_url,title,url_hash,image_url,published_at) "
+              "VALUES (2,1,'u2','T2','h2',NULL,'2026-06-01T00:00:00')")  # newest
+    c.execute("INSERT INTO article_scores (article_id,accepted) VALUES (1,1),(2,1)")
+    c.commit()
+    seen = []
+    enrich.enrich_recent_images(c, fetch=lambda url: seen.append(url) or "http://og.jpg", limit=10)
+    # both enriched; newest processed first
+    assert seen[0].endswith("u2")
+    assert c.execute("SELECT image_url FROM articles WHERE id=2").fetchone()[0] == "http://og.jpg"