Configure MCP servers to use Harbor OCI registry

- Updated Chart.yaml dependencies to use OCI registry
- Added HelmRepository resource for Harbor
- Created Harbor registry secret (SOPS-encrypted)
- Updated HelmRelease to use HelmRepository instead of Git source
- Packaged and pushed all 16 MCP charts to Harbor OCI registry
- Updated .sops.yaml to handle platform secrets

All MCP charts are now available at:
oci://images.caffeinetux.com/mcp-charts

platform/mcp-servers/helmrepository.yaml

@@ -0,0 +1,11 @@
+apiVersion: source.toolkit.fluxcd.io/v1beta2
+kind: HelmRepository
+metadata:
+  name: mcp-charts
+  namespace: flux-system
+spec:
+  type: oci
+  url: oci://images.caffeinetux.com/mcp-charts
+  interval: 5m
+  secretRef:
+    name: harbor-registry-secret