### Summary
Closes#17885.
MinerU figure enrichment now passes the resolved dataset language to
`vision_llm_figure_describe_prompt`. Missing and empty language values
use `English`, matching the other figure-description paths.
This change is limited to MinerU. PR #18021 already fixed the Mistral
path.
### Summary
Refs #17885.
Mistral figure enrichment now receives the dataset language through the
production parsing path. `by_mistral_ocr` forwards `lang` to
`MistralParser.parse_pdf`; the parser stores the normalized language and
passes it to the figure-description prompt. Empty or missing values
still fall back to English.
Ports the dataset knowledge compilation (wiki/graph/tree/mindmap) to the
Go scheduler with a status contract, aligns wiki storage/retrieval with
Python, and sizes prompts by content_length.
