chore: add Renovate config for automated dependency updates

Extends config:recommended and helpers:pinGitHubActionDigests to
keep Cargo deps and GitHub Action SHAs up to date via PRs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: h4x0r

renovate.json

@@ -0,0 +1,7 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "config:recommended",
+    "helpers:pinGitHubActionDigests"
+  ]
+}