Add snapshot selection to augment CLI

[xiao312]

Summary

• add repeatable --time snapshot selection to dfode-kit augment
• support index/slice/stride selection against ordered HDF5 snapshot keys
• include resolved snapshot names/count in preview JSON and apply results
• add tests for time selector behavior
• update augment/CLI/data-workflow docs

Examples

dfode-kit augment --source sample.h5 --mech gri30.yaml --save aug.npy --preset random-local-combustion-v1 --target-size 20000 --time 0:12 --apply

dfode-kit augment --source sample.h5 --mech gri30.yaml --save aug.npy --preset random-local-combustion-v1 --target-size 20000 --time ::10 --apply

Verification

• make verify
• make docs-build