- AppSidebar: spinner moved inside GnSearchField input-group-addon via CSS
  (:deep .input-group-addon overlay). Removed spinner from sessions-label.
- AppSidebar: closeSearch and handleSelect now call sessionsStore.exitSearch()
  and reload normal session list, so search results disappear after selection.
  toggleSearch restores previous query and re-activates search on reopen.
- CSS msg-flash: removed animation-fill-mode:both and background-color:transparent
  from keyframes, so message bubble keeps its original background after flash.
- SessionsStore: added exitSearch() method (preserves query, disables active flag).
- Tests pass (51/51)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>