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>

src/skill_seekers/cli/quality_checker.py

@@ -315,7 +315,7 @@ class SkillQualityChecker:
                 self.report.add_warning("links", f"Broken link: [{text}]({link})", "SKILL.md")
         else:
             if links:
-                internal_links = [l for t, l in links if not l.startswith("http")]
+                internal_links = [link for t, link in links if not link.startswith("http")]
                 if internal_links:
                     self.report.add_info(
                         "links", f"✓ All {len(internal_links)} internal links are valid", "SKILL.md"