fix: QOTD/WOTD freshness — pick within the freshest cohort, not the rotated pool

Both selectors ordered candidates least-recently-shown, then daily.seeded_order()
ROTATED the whole list and took [0] — an arbitrary date-hashed item, undoing the
ordering. Result: repeats (quote id 2 on 6/28+6/29; word "harmony" on 6/25+6/28),
no guarantee a pool item is shown before it recurs.

Fix: daily.freshest(rows) returns the freshest cohort only — every NEVER-shown
item while any remain, else the oldest-shown group. quote/wotd _candidates use it;
seeded_order now picks deterministically WITHIN that cohort. So every pool item is
featured once before any repeat, then cycles oldest-first. Dropped the unused
_NO_REPEAT_POOL window. Tests: no-repeat-until-exhausted (quote + wotd) + a
freshest() unit test. 428 backend tests green.

(Separate follow-up: expand the QOTD pool from 16 → 90+ vetted public-domain
quotes for a longer no-repeat window.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

goodnews/daily.py

@@ -33,6 +33,21 @@ def seeded_order(ids: list, date_str: str) -> list:
     return ids[seed:] + ids[:seed]
 
 
+def freshest(rows: list) -> list:
+    """The cohort to feature today, from pool rows carrying `id` + `shown_at`: every
+    NEVER-shown item (shown_at NULL) while any remain, else every item tied for the
+    OLDEST shown_at. Guarantees each pool item is featured ONCE before any repeat, then
+    cycles oldest-first. Pick deterministically *within* this cohort (seeded_order) —
+    NEVER across the whole pool, which re-feeds recent items (the QOTD/WOTD repeat bug)."""
+    never = [r["id"] for r in rows if r["shown_at"] is None]
+    if never:
+        return sorted(never)
+    if not rows:
+        return []
+    oldest = min(r["shown_at"] for r in rows)
+    return sorted(r["id"] for r in rows if r["shown_at"] == oldest)
+
+
 def content_key(*parts) -> str:
     """A stable dedup key for a pool item (so re-harvesting never duplicates a row)."""
     raw = "|".join("" if p is None else str(p) for p in parts)