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_lifecycle.go

@@ -95,6 +95,7 @@ func (handler *accessibilityEventHandler) handleLifecycle(event atspi.Event) boo
 			browser.loaded(event.Source.ID())
 			if objectReview != nil {
 				objectReview.ResetDocument(event.Source.ID())
+				objectReview.WarmDocument()
 			}
 		}
 		return true
@@ -134,6 +135,8 @@ func (handler *accessibilityEventHandler) handleLifecycle(event atspi.Event) boo
 				if err := objectReview.JumpToDocumentFragment(event.DocumentFragment); err != nil {
 					logger.Warn("queue document fragment navigation", "error", err)
 				}
+			} else {
+				objectReview.WarmDocument()
 			}
 		}
 		if !alreadyAnnounced {