chore: add publish-external-dists workflow + zap-mdns/zap-protocol dists

Bootstraps hanzo-tools-browser v0.5.4 dependencies on PyPI.

- zap-mdns 0.1.0 (HIP-0069 mDNS publisher/discoverer)
- zap-protocol 0.2.1 (capnp wire protocol)

.github/workflows/publish-external-dists.yml

@@ -0,0 +1,34 @@
+name: Publish External Dists
+
+# One-shot workflow: uploads any pre-built wheel/sdist staged under
+# dist-external/ to PyPI using the existing HANZO_PYPI_TOKEN / PYPI_TOKEN
+# repo secret. Used to bootstrap external deps (zap-mdns, zap-protocol)
+# whose source lives outside this repo.
+
+on:
+  workflow_dispatch:
+
+jobs:
+  upload:
+    name: Upload dist-external/* to PyPI
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Install twine
+        run: pip install --upgrade twine
+
+      - name: List dists
+        run: ls -la dist-external/
+
+      - name: Upload to PyPI
+        env:
+          TWINE_USERNAME: __token__
+          TWINE_PASSWORD: ${{ secrets.HANZO_PYPI_TOKEN || secrets.PYPI_TOKEN }}
+        run: |
+          python -m twine upload --skip-existing dist-external/*.whl dist-external/*.tar.gz