fix: harden admin and CMPP delivery workflows

api/prisma/migrations/20260715090000_track_downstream_manual_retries/migration.sql

@@ -0,0 +1,3 @@
+ALTER TABLE "CmppDownstreamDelivery"
+  ADD COLUMN "manualRetryCount" INTEGER NOT NULL DEFAULT 0,
+  ADD COLUMN "lastRetriedAt" TIMESTAMP(3);

api/prisma/migrations/20260715153000_remove_disconnected_downstream_sessions/migration.sql

@@ -0,0 +1,4 @@
+-- Downstream connection rows represent current live sessions only.
+-- Remove historical disconnected/timeout rows left by the previous persistence model.
+DELETE FROM "CmppDownstreamConnection"
+WHERE "status" <> 'connected';