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>

ideas.md

@@ -18,3 +18,5 @@ $ I really like the coloring for the metadata highlighting in each card (The gra
 
 -l Shomehow include a daily inspirational/motivational/uplifting quote that would change each day.
 - Allow ability to forward/share articles
+* Session-only history of seen/swapped-away articles, recoverable without an account  [done: History panel; Replace no longer recycles seen stories]
+| Persistent history + favorites with sign-in  [tabled: needs accounts]