chore(ci): update GitHub Actions and SHA-pin docs.yml

Updates GitHub Actions to their latest releases and switches
.github/workflows/docs.yml from floating major tags to commit-SHA pins, so
every actions/* reference is pinned by SHA with a version comment (matching
the convention used in the other workflows).

- actions/checkout          v6.0.2       -> v7.0.1  (docs.yml was already @v7)
- actions/setup-python       v6 / v6.3.0 -> v7.1.0
- actions/setup-node        v6.4.0       -> v7.1.0
- actions/upload-artifact    v7.0.1      -> v7.0.2
- actions/configure-pages                -> v6.0.0 (SHA-pinned)
- actions/upload-pages-artifact          -> v5.0.0 (SHA-pinned)
- actions/deploy-pages                   -> v5.0.1 (SHA-pinned)

peter-evans/create-pull-request (v8.1.1) and
peter-evans/enable-pull-request-automerge (v3.0.0) are already on their
latest releases and left unchanged.

Safe for our usage: checkout v7 only changes pull_request_target /
workflow_run behavior (unused here); setup-python v7 drops the unused
pip-install input (both usages pass only python-version / cache).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/docs.yml

@@ -27,12 +27,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v7
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           fetch-depth: 0
 
       - name: Set up Python
-        uses: actions/setup-python@v6
+        uses: actions/setup-python@6d4fd22b20465ccc0f7354476588e8df7c9ca0e0 # v7.1.0
         with:
           python-version: "3.x"
           cache: pip
@@ -47,10 +47,10 @@ jobs:
         run: mkdocs build --strict --config-file website/mkdocs.yml
 
       - name: Configure Pages
-        uses: actions/configure-pages@v6
+        uses: actions/configure-pages@45bfe0192ca1faeb007ade9deae92b16b8254a0d # v6.0.0
 
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v5
+        uses: actions/upload-pages-artifact@fc324d3547104276b827a68afc52ff2a11cc49c9 # v5.0.0
         with:
           path: website/site
 
@@ -63,4 +63,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v5
+        uses: actions/deploy-pages@368f82528645a54fb793d4d04e342629a3f51346 # v5.0.1