ci: simplify to single-arch amd64-only build on lux-build ARC runners

Drop arm64 + manifest jobs (cluster is amd64-only). All jobs now run
on lux-build self-hosted runners — no GitHub-hosted runners needed.
Build -> deploy in 2 jobs, no intermediate manifest step.

.github/workflows/build-lux.yml

@@ -20,8 +20,7 @@ env:
   IMAGE_NAME: luxfi/explore
 
 jobs:
-  # Build amd64 image on self-hosted DOKS lux-build runner
-  build-amd64:
+  build:
     runs-on: lux-build
     permissions:
       contents: read
@@ -53,11 +52,11 @@ jobs:
           flavor: |
             latest=false
           tags: |
-            type=raw,value=latest,enable={{is_default_branch}},suffix=-amd64
-            type=ref,event=branch,suffix=-amd64
-            type=semver,pattern={{version}},suffix=-amd64
+            type=raw,value=latest,enable={{is_default_branch}}
+            type=ref,event=branch
+            type=semver,pattern={{version}}
 
-      - name: Build and push amd64 image
+      - name: Build and push image
         id: build
         uses: docker/build-push-action@v6
         with:
@@ -73,104 +72,10 @@ jobs:
             GIT_COMMIT_SHA=${{ env.SHORT_SHA }}
             GIT_TAG=${{ github.ref_type == 'tag' && github.ref_name || '' }}
 
-  # Build arm64 image natively on ARM runner
-  build-arm64:
-    runs-on: ubuntu-24.04-arm
-    permissions:
-      contents: read
-      packages: write
-    outputs:
-      image-digest: ${{ steps.build.outputs.digest }}
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-
-      - name: Login to GitHub Container Registry
-        uses: docker/login-action@v3
-        with:
-          registry: ${{ env.REGISTRY }}
-          username: ${{ github.repository_owner }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-
-      - name: Add SHORT_SHA
-        run: echo "SHORT_SHA=$(echo ${GITHUB_SHA} | cut -c1-8)" >> $GITHUB_ENV
-
-      - name: Extract metadata
-        id: meta
-        uses: docker/metadata-action@v5
-        with:
-          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
-          flavor: |
-            latest=false
-          tags: |
-            type=raw,value=latest,enable={{is_default_branch}},suffix=-arm64
-            type=ref,event=branch,suffix=-arm64
-            type=semver,pattern={{version}},suffix=-arm64
-
-      - name: Build and push arm64 image
-        id: build
-        uses: docker/build-push-action@v6
-        with:
-          context: .
-          platforms: linux/arm64
-          labels: ${{ steps.meta.outputs.labels }}
-          tags: ${{ steps.meta.outputs.tags }}
-          cache-from: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}-cache:arm64
-          cache-to: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}-cache:arm64,mode=max
-          provenance: false
-          push: ${{ github.event_name != 'pull_request' }}
-          build-args: |
-            GIT_COMMIT_SHA=${{ env.SHORT_SHA }}
-            GIT_TAG=${{ github.ref_type == 'tag' && github.ref_name || '' }}
-
-  # Create multi-platform manifest
-  create-manifest:
-    if: github.event_name != 'pull_request'
-    runs-on: lux-build
-    permissions:
-      contents: read
-      packages: write
-    needs: [build-amd64, build-arm64]
-    steps:
-      - name: Login to GitHub Container Registry
-        uses: docker/login-action@v3
-        with:
-          registry: ${{ env.REGISTRY }}
-          username: ${{ github.repository_owner }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-
-      - name: Extract metadata for manifest
-        id: meta
-        uses: docker/metadata-action@v5
-        with:
-          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
-          flavor: |
-            latest=false
-          tags: |
-            type=raw,value=latest,enable={{is_default_branch}}
-            type=ref,event=branch
-            type=semver,pattern={{version}}
-
-      - name: Create and push manifest
-        run: |
-          TAGS=$(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON")
-          AMD64_IMAGE="${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ needs.build-amd64.outputs.image-digest }}"
-          ARM64_IMAGE="${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ needs.build-arm64.outputs.image-digest }}"
-          docker buildx imagetools create $TAGS $AMD64_IMAGE $ARM64_IMAGE
-        env:
-          DOCKER_METADATA_OUTPUT_JSON: ${{ steps.meta.outputs.json }}
-
-  # Deploy to DOKS cluster
   deploy:
     if: github.ref == 'refs/heads/main' && github.event_name != 'pull_request'
     runs-on: lux-build
-    needs: [create-manifest]
+    needs: [build]
     steps:
       - name: Install doctl
         uses: digitalocean/action-doctl@v2