refactor(tests): YAML-driven fixtures for preprocessor tests
- cases.yaml: 10 test cases con schema dichiarativo (op, assertions)
- data/: 7 file reali (email_action.html, email_thread.html, email_single.html,
email_heavy.html, generic_page.html, notes.txt, fallback.txt)
- test_preprocessors.py: parametrize da YAML via test_detect / test_preprocess;
assertion engine generico (no_html_tags, min_length, compression_ratio,
metadata_keys, contains, not_contains, content_type)
- requirements.txt: add PyYAML
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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