ci: allow manual UI triggers to run build and deploy steps

Drone's "Run" button fires a `custom` event, which the existing
`event: [push]` filter rejected, so manual re-runs cloned and exited.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: wug-ge

.drone.yml

@@ -20,6 +20,7 @@ steps:
       - main
     event:
       - push
+      - custom
 - name: publish_frontend
   image: plugins/docker
   settings:
@@ -36,6 +37,7 @@ steps:
       - main
     event:
       - push
+      - custom
 
 - name: run_tests
   image: node:24
@@ -54,6 +56,7 @@ steps:
       - main
     event:
       - push
+      - custom
   volumes:
     - name: docker_sock
       path: /var/run/docker.sock