Add Dependabot configuration for automated dependency updates (#730)

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: rscohn2

.github/dependabot.yml

@@ -0,0 +1,19 @@
+version: 2
+updates:
+  # Python dependencies for documentation
+  - package-ecosystem: "pip"
+    directory: "/docs"
+    schedule:
+      interval: "weekly"
+    commit-message:
+      prefix: "deps"
+      include: "scope"
+
+  # GitHub Actions across all workflows
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    commit-message:
+      prefix: "ci"
+      include: "scope"