Initialize Helm chart structure

[aktech]

Feature description

Set up the basic Helm chart structure with JupyterHub as a dependency. This follows the same pattern as classic Nebari - using the upstream JupyterHub Helm chart rather than creating custom Kubernetes templates.

The upstream JupyterHub Helm chart (jupyterhub/jupyterhub) handles all the complex Kubernetes resources (hub deployment, proxy, RBAC, spawner configuration). We use it as a dependency and customize via values + extraConfig files.

Tasks

• Create Chart.yaml with JupyterHub dependency (v4.3.2)
• Create basic values.yaml with schema structure
• Create templates/_helpers.tpl with common template helpers
• Create templates/NOTES.txt for post-install instructions
• Create .helmignore
• Run helm dependency update to fetch JupyterHub chart
• Clean up any existing partial implementation files

Acceptance Criteria

• helm lint . passes
• helm dependency list shows jupyterhub chart (v4.3.2)
• helm template . renders without errors

[aktech]

This is implemented as well.