Add warning when local_repo_path directory doesn't exist

[yusufkaraaslan]

Summary

Add validation to warn users when local_repo_path is provided but the directory doesn't exist.

Background

Follow-up from PR #195 - Reviewer Question #4 by @jimmy058910

Current Behavior

If user provides invalid local_repo_path, the scraper silently falls back to GitHub API mode without warning.

Desired Behavior

Display clear warning message and inform user of fallback:

if local_repo_path and not os.path.isdir(local_repo_path):
    logger.warning(f"local_repo_path does not exist: {local_repo_path}")
    logger.warning("Falling back to GitHub API mode")

Benefits

• Catches user typos in config
• Makes failure mode explicit
• Improves UX

Related

• PR feat: Add unlimited local repository analysis and fix 10 critical bugs #195 - Unlimited local repo analysis
• Issue [BUG] Cannot use skill-seekers on github repo - Error: name 'logger' is not defined #190 - Logger initialization

Files to Modify

• src/skill_seekers/cli/github_scraper.py - Add validation in init or scraping method

Priority

Low - Enhancement (non-breaking, improves UX)