Add Dependabot configuration for automated dependency updates (#187)

This commit adds Dependabot configuration to automate dependency updates for:
- Ruby gems (weekly)
- JavaScript packages (weekly)
- GitHub Actions (monthly)

This will help us keep dependencies up-to-date with security patches and new features.

Author: cirdes

.github/dependabot.yml

@@ -0,0 +1,21 @@
+version: 2
+updates:
+  # Ruby dependencies
+  - package-ecosystem: "bundler"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 10
+  # JavaScript dependencies  
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 10
+
+  # GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    open-pull-requests-limit: 5