chore: auto-assign Dependabot PRs to @cartesiosson

Adds 'assignees: [cartesiosson]' to both ecosystems so any PR opened
by Dependabot lands directly in the maintainer's review queue without
manual triage. Reviewer assignment stays in CODEOWNERS (the 'reviewers'
key is deprecated in dependabot.yml v2).

Author: cartesiosson

.github/dependabot.yml

@@ -1,6 +1,9 @@
 # Dependabot config: keeps GitHub Actions and Docker base images up to date,
 # auto-opens PRs when a CVE or new release shows up.
 # https://docs.github.com/code-security/dependabot
+#
+# Reviewers are NOT set here (the property is deprecated in v2). Reviewer
+# assignment is handled by .github/CODEOWNERS.
 
 version: 2
 updates:
@@ -11,6 +14,8 @@ updates:
       interval: weekly
       day: monday
     open-pull-requests-limit: 5
+    assignees:
+      - cartesiosson
     commit-message:
       prefix: ci
       include: scope
@@ -25,6 +30,8 @@ updates:
       interval: weekly
       day: monday
     open-pull-requests-limit: 5
+    assignees:
+      - cartesiosson
     commit-message:
       prefix: chore
       include: scope