Volt v1.2.7

Changes

• Fix: Remove self.change_query() that crashed every plan switch
• Fix: Replace self.debug() with file-based _log_error()
• Fix: Replace CLSIDFromString with pure Python guid_from_string()
• Perf: Use PowerSetActiveScheme Win32 API (no subprocess freeze)
• Add non-blocking Popen fallback if API fails
• Limit to 3 standard plans (High Performance, Balanced, Power Saver)
• Add active status icons
• Document known cache limitation in README