fix: Fix list comprehension variable names (NameError in CI)

Fixed incorrect variable names in list comprehensions that were causing
NameError in CI (Python 3.11/3.12):

Critical fixes:
- tests/test_markdown_parsing.py: 'l' → 'link' in list comprehension
- src/skill_seekers/cli/pdf_extractor_poc.py: 'l' → 'line' (2 occurrences)

Additional auto-lint fixes:
- Removed unused imports in llms_txt_downloader.py, llms_txt_parser.py
- Fixed comparison operators in config files
- Fixed list comprehension in other files

All tests now pass in CI.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tests/test_markdown_parsing.py

@@ -97,7 +97,7 @@ plain code without language
             content, "https://example.com/docs/test.md"
         )
         # Should only include .md links
-        md_links = [l for line in result["links"] if ".md" in l]
+        md_links = [link for link in result["links"] if ".md" in link]
         self.assertEqual(len(md_links), len(result["links"]))
 
     def test_extract_content_paragraphs(self):