- Extract saveResumeState helper: saves when playing OR paused (not just
  paused). Both WS and REST stop handlers now call it.
- restoreResume now jumps to saved PlaylistPos before seeking, so the
  correct track is loaded even when playlist order differs.
- Title validation: if the loaded title does not match the window title
  after jumping, abort restore and delete stale resume file.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>