ci: build ogcard image on push to main

The workflow only triggered on pull_request, which meant the image
tagged with a PR commit SHA would get pushed to ECR, but the merge
commit to main never produced a fresh image. Deploy tooling resolving
main to an ECR tag would either miss or pick up a stale PR build.

Match bskyweb-aws: `push: branches: [main]` + `workflow_dispatch`.
Drops the pull_request trigger entirely. If Dockerfile validation on
PRs is wanted back, we can add a hybrid pattern later (build-on-PR,
push-only-on-main).

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

.github/workflows/build-and-push-ogcard-aws.yaml

@@ -1,11 +1,9 @@
 name: build-and-push-ogcard-aws
 on:
   workflow_dispatch:
-  pull_request:
+  push:
-    paths:
+    branches:
-      - "bskyogcard/**"
+      - main
-      - "Dockerfile.bskyogcard"
-      - ".github/workflows/build-and-push-ogcard-aws.yaml"
 
 env:
   REGISTRY: ${{ secrets.AWS_ECR_REGISTRY_USEAST2_PACKAGES_REGISTRY }}