fix(media): retain inbound media with recursive cleanup TTL (#38292)

* Config: add media retention TTL setting

* Media: recurse persisted media cleanup

* Gateway: add persisted media cleanup timer

* Media: harden retention cleanup sweep

* Media: make recursive retention cleanup opt-in

* Media: retry writes after empty-dir cleanup race

src/media/server.ts

@@ -96,7 +96,7 @@ export function attachMediaRoutes(
 
   // periodic cleanup
   setInterval(() => {
-    void cleanOldMedia(ttlMs);
+    void cleanOldMedia(ttlMs, { recursive: false });
   }, ttlMs).unref();
 }