[Docs] AgentHarness install guide uses wrong manifest URL and broken Helm values

[tuguldur-dev]

The Enable AgentHarness support section on the installation page contains incorrect setup instructions that can cause installation failures.

Page: /docs/kagent/introduction/installation#enable-agentharness-support
File: src/app/docs/kagent/introduction/installation/page.mdx

Steps to Reproduce

1. Open the Installing kagent page.
2. Navigate to Enable AgentHarness support.
3. Follow Step 1 and run the OpenShell installation commands.

Actual Behavior

• agent-sandbox is installed from a vendored NVIDIA OpenShell manifest instead of the official upstream kubernetes-sigs/agent-sandbox release.
• The inline Helm values block contains invalid YAML:
  • disableTls is not indented under server.
  • metricsPort is not indented under service.
• The invalid YAML can cause the OpenShell installation to fail.

Expected Behavior

• The documentation should install agent-sandbox using the official upstream release manifest.
• The Helm values example should contain valid YAML with correct indentation so users can successfully install OpenShell without errors.

Suggested Fix

• Replace the vendored agent-sandbox manifest reference with the official upstream release manifest.
• Correct the Helm values block indentation:
  • Move disableTls under server.
  • Move metricsPort under service.
• Validate the installation steps end-to-end to ensure they work as documented.

Environment

• Documentation page: /docs/kagent/introduction/installation
• Observed while following the AgentHarness/OpenShell installation instructions.