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/briefs.py

@@ -9,7 +9,7 @@ from .paywall import is_paywalled
 def build_daily_brief(
     conn: sqlite3.Connection,
     brief_date: str | None = None,
-    limit: int = 5,
+    limit: int = 7,
     replace: bool = False,
     window_days: int = 3,
 ) -> int:
@@ -22,7 +22,7 @@ def build_daily_brief(
 
     brief_id = conn.execute(
         "INSERT INTO daily_briefs (brief_date, title) VALUES (?, ?)",
-        (target_date, f"Five Good Things Today - {target_date}"),
+        (target_date, f"Highlights from Today - {target_date}"),
     ).lastrowid
 
     rows = _candidate_articles(conn, target_date, window_days)