Fix archive plugins for НЭБ and Alib; add network integration tests

- html_scraper: add img_alt strategy (НЭБ titles from <img alt>), bold_text
  strategy (Alib entries from <p><b>), Windows-1251 encoding support,
  _cls_inner_texts() helper that strips inner HTML tags
- rsl: rewrite to POST SearchFilterForm[search] with CSRF token and CQL
  title:(words) AND author:(word) query format
- config: update rusneb (img_alt + correct author_class) and alib_web
  (encoding + bold_text) to match fixed plugin strategies
- tests: add tests/test_archives.py with network-marked tests for all six
  archive plugins; НЛР and ШПИЛ marked xfail (endpoints return HTTP 404)
- presubmit: exclude network tests from default run (-m "not network")

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -56,6 +56,7 @@ include = ["src", "tests", "scripts"]
 
 [tool.pytest.ini_options]
 pythonpath = ["src"]
+markers = ["network: live HTTP requests to external services (deselect with -m 'not network')"]
 
 [build-system]
 requires = ["poetry-core"]