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/config_extractor.py

@@ -291,7 +291,7 @@ class ConfigFileDetector:
 
         return None
 
-    def _infer_purpose(self, file_path: Path, config_type: str) -> str:
+    def _infer_purpose(self, file_path: Path, _config_type: str) -> str:
         """Infer configuration purpose from file path and name"""
         path_lower = str(file_path).lower()
         filename = file_path.name.lower()
@@ -582,7 +582,7 @@ class ConfigParser:
                 return prev_line[1:].strip()
         return ""
 
-    def _extract_python_docstring(self, node: ast.AST) -> str:
+    def _extract_python_docstring(self, _node: ast.AST) -> str:
         """Extract docstring/comment for Python node"""
         # This is simplified - real implementation would need more context
         return ""