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/helmrelease.yaml

@@ -8,10 +8,11 @@ spec:
   timeout: 5m
   chart:
     spec:
-      chart: ./platform/mcp-servers
+      chart: mcp-umbrella
+      version: "1.0.0"
       sourceRef:
-        kind: GitRepository
-        name: flux-system
+        kind: HelmRepository
+        name: mcp-charts
         namespace: flux-system
       interval: 5m