feat: migrate reposync to ArgoCD (#78)

Migrate repository sync cronjobs from Terragrunt to ArgoCD/Kustomize.
Adds four daily CronJobs (almalinux9-baseos, almalinux9-appstream, epel9,
openvox7) with associated PVCs and ConfigMaps in the reposync namespace.

💘 Generated with Crush

Assisted-by: Claude Sonnet 4.6 via Crush <crush@charm.land>

Reviewed-on: #78

apps/base/reposync/namespace.yaml

@@ -0,0 +1,7 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  labels:
+    app.kubernetes.io/name: reposync
+  name: reposync