[Bug]: Several commands accept `--format yaml` but emit table or plain text

[realrajaryan]

I have done the following

• I have searched the existing issues
• If possible, I've reproduced the issue using the 'main' branch of this project

Steps to reproduce

Run --format yaml on commands that accept the option:

$ container system df --format yaml
TYPE           TOTAL  ACTIVE  SIZE      RECLAIMABLE
Images         2      0       157.5 MB  157.5 MB (100%)
Containers     0      0       0 B       0 B (0%)
Local Volumes  0      0       0 B       0 B (0%)

$ container system status --format yaml
FIELD              VALUE
status             running
appRoot            /Users/ras/Downloads/test_container/audit_artifacts/container-issue-repros-20260511-101939/app-root/
installRoot        /usr/local/
logRoot            /Users/ras/Downloads/test_container/audit_artifacts/container-issue-repros-20260511-101939/log-root
apiserver.version  container-apiserver version 0.12.3 (build: release, commit: f989901)
apiserver.commit   f9899013fd43dd058fdf89709eed0b0861bfd931
apiserver.build    release
apiserver.appName  container-apiserver

$ container image list --format yaml
NAME          TAG          DIGEST
alpine        latest       5b10f432ef3da1b8d4c7eb6c...
local/alpine  issue-repro  5b10f432ef3da1b8d4c7eb6c...

$ container volume list --format yaml
NAME  TYPE  DRIVER  OPTIONS

$ container stats --no-stream --format yaml
Container ID  Cpu %  Memory Usage  Net Rx/Tx  Block I/O  Pids

Problem description

These commands accept yaml but return non-YAML output with exit status 0. A requested structured format should either be emitted correctly or rejected as unsupported.

Environment

- OS: macOS 26.4.1 (25E253)
- Xcode: Xcode 26.4.1 (17E202)
- Container: container CLI 0.12.3 (build: release, commit: f989901)

Code of Conduct

• I agree to follow this project's Code of Conduct

[tico88612]

I can take this, #1353 is prior art, but not apply in other feature.
I will try to implement this in next week.

[jglogan]

@tico88612 you got it, thanks!