feat(discover): suggest full albums only (filter singles/EPs)

Discovery's "Suggested albums" surfaced singles and EPs because
_derive_albums filtered with is_core_release (Album/Single/EP). Add a
discovery-only _album_kind_ok gate that, when discover.albumsOnly (new
config, default true), requires primary_type == "Album" with no secondary
types. is_core_release is untouched — the monitor/scan still use it.

Exposed discover.albumsOnly in the discover config route + a Discovery
settings toggle. Worker + web tests added.

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

worker/lyra_worker/discovery.py

@@ -17,6 +17,7 @@ class DiscoveryConfig:
     similar_per_seed: int = 20
     albums_per_artist: int = 1
     min_score: float = 0.0
+    albums_only: bool = True
 
     @classmethod
     def from_config(cls, config: dict) -> "DiscoveryConfig":
@@ -32,6 +33,12 @@ class DiscoveryConfig:
             except (KeyError, TypeError, ValueError):
                 return default
 
+        def _bool(key: str, default: bool) -> bool:
+            raw = config.get(key)
+            if raw is None:
+                return default
+            return str(raw).strip().lower() in _TRUE
+
         return cls(
             enabled=str(config.get("discover.enabled", "")).strip().lower() in _TRUE,
             interval_hours=_int("discover.intervalHours", 168),
@@ -39,6 +46,7 @@ class DiscoveryConfig:
             similar_per_seed=_int("discover.similarPerSeed", 20),
             albums_per_artist=_int("discover.albumsPerArtist", 1),
             min_score=_float("discover.minScore", 0.0),
+            albums_only=_bool("discover.albumsOnly", True),
         )
 
 
@@ -122,6 +130,18 @@ def _upsert_album(conn: psycopg.Connection, artist: dict, rg) -> int:
         return cur.rowcount
 
 
+def _album_kind_ok(g, albums_only: bool) -> bool:
+    """Which release groups qualify as discovery album suggestions.
+
+    Discovery-only policy: when albums_only (default), suggest full studio Albums
+    only — no Singles/EPs, no secondary types (live/compilation/etc.). Falls back
+    to the broader is_core_release (Album/Single/EP) when the toggle is off. This
+    deliberately does NOT touch is_core_release, which the monitor/scan still use."""
+    if albums_only:
+        return (g.primary_type or "") == "Album" and len(g.secondary_types or ()) == 0
+    return is_core_release(g.primary_type, g.secondary_types)
+
+
 def _derive_albums(conn: psycopg.Connection, browser: MbBrowser, surfaced: list[dict],
                    cfg: DiscoveryConfig) -> int:
     if cfg.albums_per_artist <= 0:
@@ -135,7 +155,7 @@ def _derive_albums(conn: psycopg.Connection, browser: MbBrowser, surfaced: list[
             print(f"worker: discovery album browse failed for {artist['mbid']}: {e}", flush=True)
             continue
         core = [g for g in groups
-                if is_core_release(g.primary_type, g.secondary_types) and g.rg_mbid not in have]
+                if _album_kind_ok(g, cfg.albums_only) and g.rg_mbid not in have]
         core.sort(key=lambda g: g.first_release_date or "", reverse=True)
         for rg in core[: cfg.albums_per_artist]:
             albums += _upsert_album(conn, artist, rg)