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/github_scraper.py

@@ -350,7 +350,7 @@ class GitHubScraper:
 
         except GithubException as e:
             if e.status == 404:
-                raise ValueError(f"Repository not found: {self.repo_name}")
+                raise ValueError(f"Repository not found: {self.repo_name}") from e
             raise
 
     def _get_file_content(self, file_path: str) -> str | None: