[Request]: Storage - Add `container system df` command to show storage usage for images, containers, and volumes

[realrajaryan]

Feature or enhancement request details

Add a container system df subcommand to display disk usage across images, containers, and volumes. This would provide a quick overview of storage utilization and reclaimable space within the container system.

Some basic requirements:

• Report actual on-disk capacity used by each resource type
• Account for APFS clones to avoid double-counting shared data
• Include reclaimable space metrics for unused or dangling data

Example output:

TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          10        5         15.2GB    8.1GB
Containers      8         3         2.4GB     1.8GB
Volumes         5         2         42.8GB    12.3GB

This would help users audit storage usage and identify cleanup opportunities.

We should have more discussion about what we can add/do better here. For example, how to:

• Show per-resource details (e.g. top N largest images or volumes)
• Handle reporting for shared layers or deduplicated data under APFS
• Optionally expose low-level stats (block usage, clone counts, etc.) for debugging

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