feat(navidrome): Instant Mix probe, ping identity, and AudioMuse UX

Parse type and serverVersion from Subsonic ping; persist per-server identity and
run a background Instant Mix probe (random songs + getSimilarSongs) for
Navidrome 0.60+. Hide the AudioMuse server toggle when the probe returns no
similar tracks; clear prefs when the server is no longer eligible.

Artist pages fall back to Last.fm similar artists when AudioMuse is enabled but
the server returns none. Instant Mix failures set a per-server issue flag with a
settings warning and toast. Settings description links the official plugin repo
via i18n Trans.

src/utils/subsonicServerIdentity.ts

@@ -0,0 +1,53 @@
+/** Fields from Subsonic `ping` / any `subsonic-response` root (Navidrome sets type + serverVersion). */
+export type SubsonicServerIdentity = {
+  type?: string;
+  serverVersion?: string;
+  openSubsonic?: boolean;
+};
+
+/** Result of `getRandomSongs` + `getSimilarSongs` probe (Instant Mix / agent chain). */
+export type InstantMixProbeResult = 'ok' | 'empty' | 'error' | 'skipped';
+
+const NAVIDROME_MIN_FOR_PLUGINS: [number, number, number] = [0, 60, 0];
+
+function parseLeadingSemver(version: string | undefined): [number, number, number] | null {
+  if (!version) return null;
+  const m = /^v?(\d+)\.(\d+)\.(\d+)/.exec(String(version).trim());
+  if (!m) return null;
+  return [Number(m[1]), Number(m[2]), Number(m[3])];
+}
+
+function semverGte(a: [number, number, number], b: [number, number, number]): boolean {
+  for (let i = 0; i < 3; i++) {
+    if (a[i] > b[i]) return true;
+    if (a[i] < b[i]) return false;
+  }
+  return true;
+}
+
+/**
+ * Navidrome version from ping supports the plugin system (≥ 0.60). Unknown `type` stays permissive
+ * until the first successful ping with metadata.
+ */
+export function isNavidromeAudiomuseSoftwareEligible(identity: SubsonicServerIdentity | undefined): boolean {
+  if (!identity?.type?.trim()) return true;
+  const t = identity.type.trim().toLowerCase();
+  if (t !== 'navidrome') return false;
+  const parsed = parseLeadingSemver(identity.serverVersion);
+  if (!parsed) return true;
+  return semverGte(parsed, NAVIDROME_MIN_FOR_PLUGINS);
+}
+
+/**
+ * Whether to show the per-server AudioMuse (Navidrome plugin) toggle in Settings.
+ * Uses software eligibility from ping plus an optional Instant Mix probe: if the server returns no
+ * similar tracks for several random songs, the row stays hidden (typical when no plugin / no agents).
+ */
+export function showAudiomuseNavidromeServerSetting(
+  identity: SubsonicServerIdentity | undefined,
+  instantMixProbe: InstantMixProbeResult | undefined,
+): boolean {
+  if (!isNavidromeAudiomuseSoftwareEligible(identity)) return false;
+  if (instantMixProbe === 'empty') return false;
+  return true;
+}