ci(docker): inline native multi-arch buildx (drop broken cross-org reusable)

Builds on luxfi-org ARC runners per-arch (lux-build-linux-amd64,
lux-build-linux-arm64), pushes by-digest, then assembles a multi-arch
manifest tagged with the semver release tag plus :latest. No QEMU, no
cross-org workflow_call.

.github/workflows/docker.yml

@@ -1,4 +1,10 @@
 name: Docker
+
+# Native multi-arch container build for ghcr.io/luxfi/aml on luxfi-org ARC runners.
+# No cross-org reusable, no QEMU — each arch builds on its own native runner.
+# Manifest is assembled from per-arch digests, then pushed with the
+# semver tag (on `v*` tags) or the branch alias (on main/dev/test pushes).
+
 on:
   workflow_dispatch:
   push:
@@ -9,12 +15,87 @@ permissions:
   contents: read
   packages: write
 
+env:
+  IMAGE: ghcr.io/luxfi/aml
+
 jobs:
-  docker:
-    uses: hanzoai/.github/.github/workflows/docker-build.yml@main
-    with:
-      image: ghcr.io/luxfi/aml
-      # Native multi-arch on lux-org ARC scale-sets — no QEMU.
-      runner-amd64: lux-build-linux-amd64
-      runner-arm64: lux-build-linux-arm64
-      runner-deploy: lux-build-linux-amd64
+  build:
+    name: Build ${{ matrix.arch }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - arch: amd64
+            runner: lux-build-linux-amd64
+          - arch: arm64
+            runner: lux-build-linux-arm64
+    runs-on: ${{ matrix.runner }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: docker/setup-buildx-action@v3
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Build & push by digest
+        id: build
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          platforms: linux/${{ matrix.arch }}
+          outputs: type=image,name=${{ env.IMAGE }},push-by-digest=true,name-canonical=true,push=true
+      - name: Export digest
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+      - uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ matrix.arch }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  manifest:
+    needs: build
+    runs-on: lux-build-linux-amd64
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          pattern: digests-*
+          path: /tmp/digests
+          merge-multiple: true
+      - uses: docker/setup-buildx-action@v3
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Compute tags
+        id: meta
+        run: |
+          set -e
+          tags=""
+          if [[ "${GITHUB_REF}" == refs/tags/v* ]]; then
+            v="${GITHUB_REF#refs/tags/}"
+            tags="-t ${IMAGE}:${v} -t ${IMAGE}:latest"
+          elif [[ "${GITHUB_REF}" == refs/heads/main ]]; then
+            tags="-t ${IMAGE}:main"
+          elif [[ "${GITHUB_REF}" == refs/heads/dev ]]; then
+            tags="-t ${IMAGE}:dev"
+          elif [[ "${GITHUB_REF}" == refs/heads/test ]]; then
+            tags="-t ${IMAGE}:test"
+          fi
+          echo "tags=${tags}" >> "$GITHUB_OUTPUT"
+      - name: Create + push multi-arch manifest
+        if: steps.meta.outputs.tags != ''
+        working-directory: /tmp/digests
+        shell: bash
+        run: |
+          set -e
+          digests=$(printf "${IMAGE}@sha256:%s " *)
+          docker buildx imagetools create ${{ steps.meta.outputs.tags }} ${digests}
+      - name: Inspect tagged manifest
+        if: github.ref_type == 'tag'
+        run: docker buildx imagetools inspect ${IMAGE}:${GITHUB_REF#refs/tags/}