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/llms_txt_downloader.py

@@ -1,6 +1,5 @@
 """ABOUTME: Downloads llms.txt files from documentation URLs with retry logic"""
 
-"""ABOUTME: Validates markdown content and handles timeouts with exponential backoff"""
 
 import time