### What problem does this PR solve?
This fixes a MinerU parsing failure where output JSON was not found in
nested v0.24.0 layouts, and also fixes a `content_names` NameError in
`_read_output()`. As a result, successful MinerU API runs no longer end
with false “MinerU not found” parsing failures.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)