Fix silent authentication failures and improve error handling

• Fix check_auth() to properly handle expired tokens with set -euo pipefail
• Add GLAB_PAGER='' and NO_COLOR=1 to get clean, parseable glab output
• Improve error detection for 401/invalid_token/expired/unauthorized responses
• Consolidate authentication functions (removed redundant reauthenticate)
• Replace direct glab API calls in main with dedicated auth functions
• Add check_auth_status() for non-interactive status checking
• Update detect_type() and authenticate() with consistent error handling
• Bump version to 0.2.0

Resolves issue where shuck would silently fail with expired PATs instead of prompting users to re-authenticate.