perf(database): index ProjectAlert.channelId so alert-channel deletes stop seq-scanning

Author: ericallam

.server-changes/project-alert-channel-id-index.md

@@ -0,0 +1,6 @@
+---
+area: webapp
+type: improvement
+---
+
+Deleting an alert channel is now fast and no longer slows down as a project builds up alert history.

internal-packages/database/prisma/migrations/20260810120000_add_project_alert_channel_id_index/migration.sql

@@ -0,0 +1,2 @@
+-- CreateIndex
+CREATE INDEX CONCURRENTLY IF NOT EXISTS "ProjectAlert_channelId_idx" ON "public"."ProjectAlert"("channelId");

internal-packages/database/prisma/schema.prisma

@@ -2412,6 +2412,8 @@ model ProjectAlert {
 
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
+
+  @@index([channelId])
 }
 
 enum ProjectAlertType {