Add user-configurable timezone and 12/24-hour preferences, then wire them through settings, runtime snapshots, scheduler payloads, wait handling, notifications, backups, memory, plugin metadata, and frontend formatters.
Keep UTC as the boundary for absolute instants while serializing user-facing dates in the configured or browser-resolved timezone. Preserve scheduler wall-clock inputs in the selected timezone, propagate TZ into desktop/runtime process environments, and restart active desktop sessions when the runtime timezone changes.
Cover the risky paths with timezone regression tests for settings normalization, auto and fixed timezone resolution, scheduler round-trips, memory timestamp conversion, and desktop timezone sync.
- Rename /state_sync namespace to /webui throughout codebase
- Remove get_event_types() from WebSocketHandler - handlers now process all events for their namespace
- Replace per-event handler registration with namespace-wide registration
- Add validate_event_type() class method for runtime event name validation
- Update UserMessage instantiation to use keyword arguments (message=, attachments=)
- Move send_data
