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>

scripts/presubmit.py

@@ -24,7 +24,7 @@ def presubmit():
         ["black", "--check", "."],
         ["flake8", "."],
         ["pyright"],
-        ["pytest", "tests/"],
+        ["pytest", "tests/", "-m", "not network"],
         # JS: tests run via Node built-in runner (no npm packages needed)
         ["node", "--test", "tests/js/pure-functions.test.js"],
     ]