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/mcp/server_fastmcp.py

@@ -1156,7 +1156,7 @@ async def run_http_server(host: str, port: int):
         from starlette.responses import JSONResponse
         from starlette.routing import Route
 
-        async def health_check(request):
+        async def health_check(_request):
             """Health check endpoint."""
             return JSONResponse(
                 {