feat: add SDK release notification workflow

.github/workflows/notify-sdks.yml

@@ -0,0 +1,40 @@
+# Copyright 2026 UCP Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: SDK Release Notification
+
+on:
+  push:
+    tags:
+      - 'v[0-9]+.[0-9]+.[0-9]+'
+
+jobs:
+  notify-sdks:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Notify Python SDK
+        uses: peter-evans/repository-dispatch@v3
+        with:
+          token: ${{ secrets.CROSS_REPO_READ_PAT }}
+          repository: Universal-Commerce-Protocol/python-sdk
+          event-type: spec-release
+          client-payload: '{"version": "${{ github.ref_name }}"}'
+
+      - name: Notify JavaScript SDK
+        uses: peter-evans/repository-dispatch@v3
+        with:
+          token: ${{ secrets.CROSS_REPO_READ_PAT }}
+          repository: Universal-Commerce-Protocol/js-sdk
+          event-type: spec-release
+          client-payload: '{"version": "${{ github.ref_name }}"}'