feat(packaging): nest protocol/ + ocf/ under smartthings_local, add PyPI packaging

Nest the two library packages under a single import namespace so they
can ship as one distribution:

  protocol/ -> smartthings_local/protocol/
  ocf/      -> smartthings_local/ocf/   (git mv, history preserved)

- Rewrite all imports protocol.* -> smartthings_local.protocol.*,
  ocf.* -> smartthings_local.ocf.* across the ocf modules, mqtt_demo/
  (bridge, descriptor, samples), and tests.
- Add pyproject.toml: dist name `smartthings-local`, hatch-vcs versioning
  from v* tags, wheel ships only smartthings_local/.
- Add .github/workflows/publish.yml: build + PyPI Trusted Publishing on
  v* tags (OIDC, no stored token).
- Force-include protocol/ocf_root_ca.pem via [tool.hatch.build] artifacts:
  it is tracked but matches .gitignore's *.pem, so hatchling's VCS file
  selection would drop it — and dtls_session.py loads it at runtime.
- Update mqtt_demo Dockerfile COPY and deploy.sh tar allowlist to the
  single smartthings_local/ package.
- .gitignore: build artifacts (_version.py, dist/, *.egg-info/).

Validated: pytest tests/ (11 passed), python -m build produces sdist +
wheel with the pem bundled, fresh pip install resolves all nested imports
with the pem readable from site-packages.

mqtt_demo/Dockerfile

@@ -8,9 +8,8 @@ RUN pip install --no-cache-dir -r requirements.txt
 
 # Application code — build context is the repo root (see
 # docker-compose.yml's `context: ..`) since mqtt_demo/ depends on the
-# protocol/ and ocf/ library packages that live alongside it.
-COPY protocol/ ./protocol/
-COPY ocf/ ./ocf/
+# smartthings_local library package that lives alongside it.
+COPY smartthings_local/ ./smartthings_local/
 COPY mqtt_demo/ ./mqtt_demo/
 
 # /config holds the ab0b0ac4 client cert + key. Mount from the host so