room-server: drive push engine on a timer + cut delivery latency

Two hardware-found fixes after on-air testing on the GAT562 kit:

- Add a 500ms push timer in main_room_server.cpp so the post-sync
  engine advances at its intended cadence. ZephCore is event-driven
  (no Arduino superloop), so without this the engine only ran on the
  5s housekeeping tick — posts dripped out every ~5s and transmits
  bunched up, causing timeouts/resends.

- Lower the post-sync hold from upstream's conservative defaults
  (POST_SYNC_DELAY 6s -> 2s, PUSH_NOTIFY 2000ms -> 1000ms). These are
  server-side timing only (no wire-format change), and take measured
  delivery from ~6-7s down to ~2s.

Verified on hardware (910.525/62.5/SF7/CR8, two clients): normal-pace
messages deliver in ~2s with clean ACKs. Rapid-fire bursts can still
drop out-of-order messages via the per-client timestamp replay check
(unchanged from upstream) — left as-is to stay upstream-compatible.

zephcore/app/RoomServerMesh.cpp

@@ -86,13 +86,15 @@ static void uplink_time_sync_cb(uint32_t unix_ts)
 #define SERVER_RESPONSE_DELAY       300
 #define TXT_ACK_DELAY               200
 
-/* Room server: post push/sync timing (matches upstream MeshCore). */
-#define PUSH_NOTIFY_DELAY_MILLIS    2000
+/* Room server: post push/sync timing. Upstream defaults are conservative
+ * (PUSH_NOTIFY 2000, POST_SYNC 6) which adds ~6-7s of delivery lag; lowered
+ * here for a more responsive room without changing wire formats. */
+#define PUSH_NOTIFY_DELAY_MILLIS    1000
 #define SYNC_PUSH_INTERVAL          1200
 #define PUSH_ACK_TIMEOUT_FLOOD      12000
 #define PUSH_TIMEOUT_BASE           4000
 #define PUSH_ACK_TIMEOUT_FACTOR     2000
-#define POST_SYNC_DELAY_SECS        6
+#define POST_SYNC_DELAY_SECS        2
 
 /* Stats blob returned for REQ_TYPE_GET_STATUS on a room server.  Mirrors the
  * repeater's RepeaterStats but reports posted/pushed counts in the trailing