feat(infra): add TTL cleanup worker for append-only tables

Periodically prune old read notifications, revoked/expired auth sessions,
and admin_audit in chunked transactions; wire under eventhub config.

src/infra/infra_sup.erl

@@ -56,6 +56,12 @@ init([]) ->
       restart => permanent,
       shutdown => 5000,
       type => worker,
-      modules => [subscription_worker]}
+      modules => [subscription_worker]},
+    #{id => infra_cleanup,
+      start => {infra_cleanup, start_link, []},
+      restart => permanent,
+      shutdown => 5000,
+      type => worker,
+      modules => [infra_cleanup]}
   ],
-  {ok, {SupFlags, Children}}.
+  {ok, {SupFlags, Children}}.