Closed project nodes don't have status info in topology JSON.
Add open_project_nodes and closed_project_nodes counts to
help clarify why by_status may be empty.
Open projects store Node/Link objects, but closed projects store
dictionaries loaded from topology JSON. This fix checks the type
before accessing attributes.
Return aggregated statistics:
- computes: per-compute CPU/memory/disk stats (existing)
- projects: total, opened, closed counts
- nodes: total count with breakdown by type and status
- links: total count with capturing count
