Add NEXUS AI to MCP resources

[saifelyzal]

Adds NEXUS AI to the MCP Resources list as an MCP-native application platform for deploying and operating full-stack containerized apps with MCP tools for deployments, databases, workers, storage, backups, metrics, and rollbacks.

[saifelyzal]

The failing check-readme-only job appears to be an upstream workflow permissions issue rather than a failure in this README change. This PR only modifies README.md, and the build/test jobs are passing.\n\nThe workflow calls github.rest.issues.addLabels(), github.rest.issues.createComment(), and related issue APIs, but the job currently grants only:\n\nyaml\npermissions:\n contents: read\n pull-requests: write\n\n\nBecause PRs are issues in GitHub's API model, those calls need:\n\nyaml\npermissions:\n contents: read\n pull-requests: write\n issues: write\n\n\nThe handle-confirmation job also uses github.rest.issues.* APIs and likely needs issues: write as well.