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/pdf_scraper.py

@@ -431,7 +431,8 @@ class PDFToSkillConverter:
             f.write("---\n\n")
             f.write("**Generated by Skill Seeker** | PDF Documentation Scraper\n")
 
-        line_count = len(open(filename, encoding="utf-8").read().split("\n"))
+        with open(filename, encoding="utf-8") as f:
+            line_count = len(f.read().split("\n"))
         print(f"   Generated: {filename} ({line_count} lines)")
 
     def _format_key_concepts(self) -> str: