ci: add block-proxy to Docker build workflow

Add block-proxy to the service matrix and trigger on docker/block-proxy branch
so the Rust block-proxy image gets built and pushed to ghcr.io alongside
the existing indexer images.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: andrewklau

.github/workflows/workflow-build.yaml

@@ -1,7 +1,7 @@
 name: Build Docker Images
 on:
   push:
-    branches: ['main', 'feat/api']
+    branches: ['main', 'feat/api', 'docker/block-proxy']
 jobs:
   build-deploy:
     runs-on: ubuntu-latest
@@ -27,6 +27,7 @@ jobs:
             indexer-contract,
             explorer-selector,
             aggregates,
+            block-proxy,
           ]
       fail-fast: false
     steps: