fix: include downloaded path in persist_downloaded_model_config warning

[kapil971390]

Motivation

While reviewing recent commits, I noticed that when persist_downloaded_model_config fails (e.g. disk full, permission error, network issue fetching the config template), the existing warning only logs the exception message:

Failed to persist downloaded pipeline model config to /home/user/mineru.json: [Errno 28] No space left on device

The models themselves were downloaded successfully, but the path is never written to models-dir in the config. On the next run, get_existing_configured_model_root finds no config entry and falls through to _snapshot_download_cached, triggering a full re-download — silently, with no indication of why.

Modification

Extended the warning message in persist_downloaded_model_config to include:

1. The path where models were successfully downloaded (model_root)
2. An explanation that MinerU will re-download on the next run without this entry
3. The exact JSON snippet the user can paste into their config file to avoid re-downloading

Example of the new warning:

Failed to persist downloaded pipeline model config to /home/user/mineru.json: [Errno 28] No space left on device.
Models were downloaded successfully to '/home/user/.cache/huggingface/hub/...' but the path will not be
cached, so MinerU may re-download on the next run. To avoid this, manually add the following to /home/user/mineru.json:
  "models-dir": {"pipeline": "/home/user/.cache/huggingface/hub/..."}

No logic changes — the exception is still caught and the download result is still returned normally.

BC-breaking

No. This is a warning message change only. All existing behaviour is preserved.

Checklist

Before PR:

• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests.
• Pre-commit or other linting tools are used to fix the potential lint issues.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

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[kapil971390]

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