Phase accel ESP-NOW TX into 1 ms slots from Discover sync.

Master broadcasts master_time_us; slaves schedule sends at
offset_ms=(assigned_id-1)%8 so concurrent streams collide less.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/esp_now_master.c

@@ -730,6 +730,7 @@ static void discover_task(void *param) {
 
   while (1) {
     msg.payload.discover.master_ota_pending = ota_session_busy();
+    msg.payload.discover.master_time_us = (uint64_t)esp_timer_get_time();
     if (!ota_espnow_distribution_active()) {
       esp_now_core_send_fast(ESPNOW_BCAST, &msg);
     }