- AppSidebar: use i.ph selector + !important for spinner overlay on
  input-group-addon icon. Add transition for smooth fade.
- SessionList: simplify DynamicScroller :key to 'search'/'all' only,
  removing sessions.length to prevent scroll reset on fetchMore.
- SessionList: pass empty searchQuery when searchActive is false,
  preventing stale highlights in normal session list.
- Tests pass (51/51)

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