ci: add Dependabot and pin all Actions to commit SHAs

.github/dependabot.yml

@@ -0,0 +1,14 @@
+# Keep dependencies fresh: SwiftPM packages and the GitHub Actions used in CI.
+# Actions are pinned to commit SHAs in the workflows; Dependabot understands
+# the trailing `# vN` comment and keeps both the SHA and the comment updated.
+version: 2
+updates:
+  - package-ecosystem: swift
+    directory: /
+    schedule:
+      interval: weekly
+
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly

.github/workflows/ci.yml

@@ -19,10 +19,10 @@ jobs:
         # macOS 15+ SDK to compile, macos-14 cannot build it.
         os: [macos-15, macos-26]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Cache SwiftPM
-        uses: actions/cache@v4
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4
         with:
           path: |
             .build

.github/workflows/pages.yml

@@ -23,9 +23,9 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: "3.x"
 
@@ -46,7 +46,7 @@ jobs:
           cp docs/index.html docs/privacy.html docs/logo.png docs/screenshot*.png _site/
           cp -r site/. _site/guide/
 
-      - uses: actions/upload-pages-artifact@v3
+      - uses: actions/upload-pages-artifact@56afc609e74202658d3ffba0e8f6dda462b719fa # v3
         with:
           path: _site
 
@@ -58,4 +58,4 @@ jobs:
       url: ${{ steps.deployment.outputs.page_url }}
     steps:
       - id: deployment
-        uses: actions/deploy-pages@v4
+        uses: actions/deploy-pages@d6db90164ac5ed86f2b6aed7e0febac5b3c0c03e # v4