Make paywalls systemic + fix ArticleCard reactivity

- ArticleCard: derive safeHref from article.url and reset image-failure state
  when the article changes, so in-place replacements re-evaluate correctly
  (clears the Svelte capture warning; build is warning-free again).
- Downweight paywalled stories below readable ones (stable sort) when composing
  the daily five and in feed results — the brief now leads readable and rarely
  hands over a locked door.
- review_sources gains a 'paywall-heavy' advisory flag (Nature, New Scientist
  flag at 100%); never auto-deactivates.
- New Scientist/Nature kept active but no longer reach the daily five; they
  remain browsable with the label + Replace.
- Tests: brief readability preference + paywall-heavy flag (79 total).

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

tests/test_brief_paywall.py

@@ -0,0 +1,36 @@
+from datetime import date
+
+from goodnews.db import connect, init_db
+from goodnews.briefs import build_daily_brief, show_brief
+from goodnews.paywall import is_paywalled
+
+
+def test_brief_prefers_readable_over_higher_scored_paywalled():
+    c = connect(":memory:"); init_db(c)
+    today = date.today().isoformat()
+    for sid in range(1, 8):
+        c.execute("INSERT INTO sources (id,name,feed_url,trust_score) VALUES (?,?,?,5)",
+                  (sid, f"S{sid}", f"http://s{sid}/f"))
+
+    def add(aid, sid, url, score):
+        c.execute("INSERT INTO articles (id,source_id,canonical_url,title,published_at,url_hash) "
+                  "VALUES (?,?,?,?,?,?)", (aid, sid, url, f"t{aid}", today + "T12:00:00+00:00", f"h{aid}"))
+        c.execute("INSERT INTO article_scores (article_id,constructive_score,agency_score,human_benefit_score,"
+                  "cortisol_score,ragebait_score,pr_risk_score,accepted,topic,flavor) "
+                  "VALUES (?,?,?,?,0,0,2,1,'science','discovery')", (aid, score, score, score))
+
+    # Paywalled ones are scored HIGHER — readability must still win for the five.
+    add(1, 1, "https://www.newscientist.com/a", 9)
+    add(2, 2, "https://www.nature.com/b", 9)
+    add(3, 3, "https://phys.org/c", 4)
+    add(4, 4, "https://www.goodnewsnetwork.org/d", 4)
+    add(5, 5, "https://e360.yale.edu/e", 4)
+    add(6, 6, "https://news.mongabay.com/f", 4)
+    add(7, 7, "https://theconversation.com/g", 4)
+    c.commit()
+
+    build_daily_brief(c, brief_date=today, limit=5, replace=True)
+    urls = [r["canonical_url"] for r in show_brief(c, brief_date=today, limit=10)]
+    c.close()
+    assert len(urls) == 5
+    assert not any(is_paywalled(u) for u in urls)  # five readable chosen over paywalled

tests/test_review_paywall.py

@@ -0,0 +1,25 @@
+import pytest
+from datetime import datetime, timezone
+
+from goodnews.db import connect, init_db
+from goodnews.sources import review_sources
+
+
+@pytest.fixture
+def conn():
+    c = connect(":memory:"); init_db(c)
+    c.execute("INSERT INTO sources (id,name,feed_url,trust_score) VALUES (1,'Pay','http://p/f',5)")
+    yield c; c.close()
+
+
+def test_paywall_heavy_flagged(conn):
+    now = datetime.now(timezone.utc).isoformat()
+    for i in range(20):
+        url = f"https://www.newscientist.com/{i}" if i < 15 else f"https://phys.org/{i}"
+        conn.execute("INSERT INTO articles (id,source_id,canonical_url,title,published_at,url_hash) "
+                     "VALUES (?,1,?,?,?,?)", (i, url, f"t{i}", now, f"h{i}"))
+        conn.execute("INSERT INTO article_scores (article_id,cortisol_score,ragebait_score,accepted) "
+                     "VALUES (?,1,0,1)", (i,))
+    conn.commit()
+    flagged = review_sources(conn)
+    assert flagged and "paywall-heavy" in flagged[0]["reason"]