Crisp hero (prefer og:image), 7-card Highlights, no-recycle Replace + session History

- Hero blur fix: brief enrichment now prefers a page's og:image even when a
  feed thumbnail exists (feed thumbs are often tiny; the hero is shown large).
  Verified: BBC hero upgrades to the 1024px share image, ScienceDaily to 1920px.
- Today is now 'Highlights from Today' — hero + 6 (brief size 7), which also
  makes the secondary grid a balanced 3+3 instead of an orphaned 3+1.
- Replace now excludes every article seen this session (a client-side seen-set),
  so it never cycles back to something already shown.
- New session History panel (this tab only, no account): lists everything seen,
  including swapped-away stories, so they stay recoverable. Persistent
  history/favorites are tabled for sign-in later.

Tests: og:image upgrade of an existing feed image (86 total).

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

goodnews/enrich.py

@@ -127,13 +127,16 @@ def enrich_brief_images(conn: sqlite3.Connection, brief_date: str, fetch=fetch_o
     stamps image_checked_at either way so failures are not retried forever.
     Returns how many images were newly found.
     """
+    # Brief items not yet checked. We fetch even when a feed image exists,
+    # because feed thumbnails are often tiny and the hero is shown large — a
+    # page's og:image (the social-share image) is the better hero visual.
     rows = conn.execute(
         """
         SELECT a.id, a.canonical_url
         FROM daily_briefs b
         JOIN daily_brief_items bi ON bi.brief_id = b.id
         JOIN articles a ON a.id = bi.article_id
-        WHERE b.brief_date = ? AND a.image_url IS NULL AND a.image_checked_at IS NULL
+        WHERE b.brief_date = ? AND a.image_checked_at IS NULL
         ORDER BY bi.rank
         LIMIT ?
         """,