feat: add initial_delay_minutes to reconciler for LB stagger 🕐

Configurable startup delay before the first reconciliation pass so that
multiple receivers behind a load balancer can be offset without relying
on container start order (which is lost on reboot). Set to half the
interval on the secondary receiver — e.g. interval 60m → delay 30m.
Default is 0 (no change to existing behaviour). Stop event is respected
during the delay so the worker shuts down cleanly even mid-wait.

tests/test_reconciler.py

@@ -175,6 +175,17 @@ def test_no_servers_does_not_start(delete_queue):
     assert not w.is_alive
 
 
+def test_initial_delay_stored(delete_queue):
+    cfg = {**BASE_CONFIG, "initial_delay_minutes": 30}
+    w = ReconciliationWorker(delete_queue, cfg)
+    assert w._initial_delay == 30 * 60
+
+
+def test_zero_initial_delay_by_default(delete_queue):
+    w = ReconciliationWorker(delete_queue, BASE_CONFIG)
+    assert w._initial_delay == 0
+
+
 # ---------------------------------------------------------------------------
 # _heal_backends — Option C backend healing
 # ---------------------------------------------------------------------------