fix(core): harden RedBox and autocompleter dialog DOM handling

[TDannhauer]

Summary

• Fix RedBox and autocompleter DOM handling that prevented dialog overlays from reopening cleanly
• Avoid destructive Element#update() when moving dialog HTML into RB_window
• Harden PrettyAutocompleter and KeyNavList teardown against detached nodes

Motivation

Kronolith's event edit dialog uses RedBox with PrettyAutocompleter fields for attendees and tags. After closing the dialog once, reopening failed with parentNode is null errors from removeChild, leaving overlays and autocompleter state inconsistent.

Changes

• redbox.js: replace RB_window.update(html) with a non-destructive move that parks previous children on document.body
• prettyautocomplete.js: re-init when box/input is detached; guard removeItemNode(), updateInput(), and currentEntries(); remove orphaned box nodes before rebuild
• keynavlist.js: guard destroy() when dropdown nodes are already detached

Companion PR in horde/kronolith wires these fixes into the event dialog lifecycle.

Test plan

• In Kronolith, open/close/reopen event dialogs with attendee and tag autocompleters populated
• Verify no JavaScript console errors on second and third open
• Smoke-test other RedBox dialogs (tasks, calendars) still open and close normally