ci: add Dependabot version updates for actions and uv

.github/dependabot.yml

@@ -0,0 +1,37 @@
+version: 2
+
+# Dependabot version updates. Security updates run separately and need no
+# config; this file adds routine "stay current" PRs so action majors and
+# Python deps don't silently drift out of date between security advisories.
+updates:
+  # GitHub Actions referenced by ci.yml / release.yml. Grouped into one PR
+  # so a weekly refresh of all actions is a single review, not six.
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly
+      day: monday
+    commit-message:
+      prefix: ci
+    groups:
+      actions:
+        patterns:
+          - "*"
+    open-pull-requests-limit: 5
+
+  # Python dependencies (uv-managed; pyproject.toml + uv.lock at the root).
+  # Minor and patch bumps ride together in one PR; majors open individually
+  # so breaking changes get isolated review.
+  - package-ecosystem: uv
+    directory: /
+    schedule:
+      interval: weekly
+      day: monday
+    commit-message:
+      prefix: chore(deps)
+    groups:
+      python-minor-patch:
+        update-types:
+          - minor
+          - patch
+    open-pull-requests-limit: 5