feat: add composite action for docker buildx setup

action.yml

@@ -0,0 +1,74 @@
+name: "Setup Buildx (tiny)"
+description: "Create & optionally use a docker buildx builder with an optional random name."
+inputs:
+  name:
+    description: "Builder name. If empty, a random name is generated."
+    required: false
+    default: ""
+  use:
+    description: "Whether to set the builder as current (default: true)."
+    required: false
+    default: "true"
+  driver:
+    description: "Buildx driver (default: docker-container)."
+    required: false
+    default: "docker-container"
+  image:
+    description: "Optional BuildKit image (e.g. moby/buildkit:v0.15.2). If empty, not passed."
+    required: false
+    default: ""
+outputs:
+  name:
+    description: "The effective builder name."
+    value: ${{ steps.main.outputs.name }}
+runs:
+  using: "composite"
+  steps:
+    - id: main
+      shell: bash
+      run: |
+        set -euo pipefail
+
+        # Inputs
+        IN_NAME="${{ inputs.name }}"
+        IN_USE="${{ inputs.use }}"
+        IN_DRIVER="${{ inputs.driver }}"
+        IN_IMAGE="${{ inputs.image }}"
+
+        # Generate random name if empty (lowercase, 8 chars)
+        if [[ -z "${IN_NAME}" ]]; then
+          if command -v uuidgen >/dev/null 2>&1; then
+            RAND="$(uuidgen | tr 'A-Z' 'a-z' | tr -cd 'a-z0-9' | cut -c1-8)"
+          else
+            RAND="$(head -c 12 /dev/urandom | tr -cd 'a-z0-9' | cut -c1-8)"
+          fi
+          BUILDER_NAME="builder-${RAND}"
+        else
+          BUILDER_NAME="${IN_NAME}"
+        fi
+
+        # Compose driver-opts if image provided
+        DRIVER_OPTS=()
+        if [[ -n "${IN_IMAGE}" ]]; then
+          DRIVER_OPTS+=(--driver-opt "image=${IN_IMAGE}")
+        fi
+
+        # If builder exists: optionally use it; else create it
+        if docker buildx inspect "${BUILDER_NAME}" >/dev/null 2>&1; then
+          echo "ℹ️  Builder '${BUILDER_NAME}' already exists."
+          if [[ "${IN_USE}" == "true" ]]; then
+            docker buildx use "${BUILDER_NAME}"
+            echo "✅ Using existing builder: ${BUILDER_NAME}"
+          fi
+        else
+          CMD=(docker buildx create --name "${BUILDER_NAME}" --driver "${IN_DRIVER}" "${DRIVER_OPTS[@]}")
+          if [[ "${IN_USE}" == "true" ]]; then
+            CMD+=("--use")
+          fi
+          echo "+ ${CMD[*]}"
+          "${CMD[@]}"
+          echo "✅ Created${IN_USE:+ and using} builder: ${BUILDER_NAME}"
+        fi
+
+        # Output for downstream steps
+        echo "name=${BUILDER_NAME}" >> "$GITHUB_OUTPUT"