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>

web/src/app/api/discover/config/route.ts

@@ -5,6 +5,7 @@ const DEFAULTS: Record<string, string> = {
   "discover.intervalHours": "168",
   "discover.similarPerSeed": "20",
   "discover.albumsPerArtist": "1",
+  "discover.albumsOnly": "true",
   "discover.minScore": "0",
   "discover.chunkSize": "5",
   "discover.listenBrainzUrl": "",

web/src/app/settings/settings-form.tsx

@@ -394,6 +394,7 @@ export function SettingsForm() {
               artists are processed per worker cycle (keeps job-claiming responsive on big rosters).
               <b> Similar per seed</b> — candidates pulled per artist. <b>Albums per artist</b> —
               releases surfaced per suggested artist. <b>Min score</b> — drops weak suggestions.{" "}
+              <b>Albums only</b> — suggest full-length albums only, hiding singles and EPs.{" "}
               <b>ListenBrainz base URL</b> — leave blank for the default endpoint.
             </HelpButton>
           </div>
@@ -405,6 +406,14 @@ export function SettingsForm() {
               </label>
             ))}
           </div>
+          <label className="toggle" style={{ margin: "10px 0 0" }}>
+            <input
+              type="checkbox"
+              checked={discoverCfg["discover.albumsOnly"] !== "false"}
+              onChange={(e) => setCfg("discover.albumsOnly", e.target.checked ? "true" : "false")}
+            />
+            Albums only (hide singles &amp; EPs)
+          </label>
           <label className="field">
             <span>ListenBrainz base URL (blank = default)</span>
             <input value={discoverCfg["discover.listenBrainzUrl"] ?? ""}