ci: Use poe tasks for model generation in CI workflow (#705)

## Summary

- Add `generate-models-from-file` poe task that accepts a local file
path, working around `datamodel-codegen` ignoring `--input` when `url`
is set in `pyproject.toml`
- Update CI workflow to call poe tasks instead of `datamodel-codegen`
directly, ensuring the downloaded artifact from apify-docs PRs is
actually used

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>