Make web document navigation survive live-updating pages

Recreated-node caret recovery, tolerant caret validation, per-root retained document trees and cursors across tab switches, document warm-up, coalesced structural moves, and hung-provider fast-fail with an 'Application is not responding' announcement.

internal/app/event_browser_tabs.go

@@ -47,7 +47,8 @@ func (handler *accessibilityEventHandler) handleBrowserTab(event atspi.Event, ac
 			if state.current.Autocomplete {
 				focus = state.current.ID()
 			}
-			objectReview.ResetDocument(focus)
+			objectReview.SuspendDocument(focus)
+			objectReview.WarmDocument()
 		}
 		spoken := presentation.FocusSpeechWithOptions(event.Source, state.presentationOptions)
 		text := spoken.Text