feat: separate writable data dir from program dir (LAN update groundwork)

- add get_data_dir() with CMBOT_DATA_DIR override, fallback to program dir
- point config/logs/output at the data root; resources stay on program root
- harden config/template writes with parents=True for a deep data root
- add docs/10-lan-update.md (LAN auto-update design); default install root
  %LOCALAPPDATA%\CMBot for elevation-free self-update

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/services/config_service.py

@@ -56,7 +56,7 @@ def save_config(data):
     config_file = get_config_path(_CONFIG_FILENAME)
 
     try:
-        config_file.parent.mkdir(exist_ok=True)
+        config_file.parent.mkdir(parents=True, exist_ok=True)
         with open(str(config_file), "w", encoding="utf-8") as f:
             json.dump(data, f, ensure_ascii=False, indent=2)
         logger.info("Config saved to %s", config_file)