hotfix: disable GitHub MCP sidecar - image doesn't exist

The GitHub MCP server has been archived and moved to servers-archived repo.
There is no Docker image available at ghcr.io/modelcontextprotocol/servers/github.

Disabling by default to prevent ImagePullBackOff errors.

TODO: Either build custom image from archived source or find alternative.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

chart/values.yaml

@@ -109,7 +109,7 @@ mcpSidecars:
         memory: "256Mi"
         cpu: "500m"
   github:
-    enabled: true  # Enabled by default, uses GITHUB_TOKEN from env
+    enabled: false  # DISABLED: GitHub MCP server has been archived, image doesn't exist
     image:
       repository: ghcr.io/modelcontextprotocol/servers/github
       tag: latest  # Update to specific version once available