fix(ci): restore SHA-pins that were accidentally reverted to mutable tags

Reverts two accidental mutable-tag changes introduced in this branch:
- pypa/gh-action-pypi-publish: release/v1 -> cef22109... (matches #276 intent)
- actions/checkout: @v6 -> de0fac2e... (matches #276 intent)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/publish-runtime.yml

@@ -180,7 +180,7 @@ jobs:
         # environment pypi-publish. The action mints a short-lived OIDC
         # token and exchanges it for a PyPI upload credential — no static
         # API token in this repo's secrets.
-        uses: pypa/gh-action-pypi-publish@release/v1
+        uses: pypa/gh-action-pypi-publish@cef221092ed1bacb1cc03d23a2d87d1d172e277b # release/v1
         with:
           packages-dir: ${{ runner.temp }}/runtime-build/dist/
 

.github/workflows/secret-pattern-drift.yml

@@ -48,7 +48,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 5
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
       - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
         with: