v9.2.7: fix startup double-load blink + device switch resolution

- _update_theme_directories() returns True on first-install auto-load;
  apply_device_config() skips restore_last_theme() to avoid double-send
- Re-activating an LCD device now sets global resolution + refreshes
  theme directories

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>