refactor: change data directory from .coin-hunter to .coinhunter

- Update SKILL.md references to use ~/.coinhunter/
- Update user-data-layout.md with new directory paths
- Update init_user_state.py ROOT path
- Unify naming convention with .stockbuddy style

scripts/init_user_state.py

@@ -3,7 +3,7 @@ import json
 from datetime import datetime, timezone
 from pathlib import Path
 
-ROOT = Path.home() / ".coin-hunter"
+ROOT = Path.home() / ".coinhunter"
 CACHE_DIR = ROOT / "cache"