fix(discover): hide stale singles + replace album set on re-derive

- Client filters the row's album thumbnails to full albums only (hides
  singles/EPs left over from pre-albums-only sweeps).
- Worker: re-deriving an artist deletes its pending album suggestions that are
  no longer picks (stale singles / now-owned), keeping wanted/dismissed rows,
  so the suggestion set self-cleans instead of accumulating.

worker 246, web 189 tests.

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

worker/lyra_worker/discovery.py

@@ -217,6 +217,16 @@ def _derive_albums(conn: psycopg.Connection, browser: MbBrowser, surfaced: list[
         if popular is not None:
             reasons[popular] = "newest,popular" if reasons.get(popular) == "newest" else "popular"
 
+        # Re-deriving replaces this artist's album set: drop any pending album suggestion of
+        # theirs that is no longer a pick (stale singles/EPs from older sweeps, or an album now
+        # owned), keeping wanted/dismissed rows untouched. Then upsert the current picks.
+        with conn.cursor() as cur:
+            cur.execute(
+                "DELETE FROM \"DiscoverySuggestion\" WHERE kind = 'album' AND status = 'pending' "
+                'AND "artistMbid" = %s AND NOT ("rgMbid" = ANY(%s))',
+                (artist["mbid"], list(reasons.keys())),
+            )
+
         for rg in core:  # preserve newest-first order among the chosen
             reason = reasons.get(rg.rg_mbid)
             if reason is not None: