fix(visualization): keep loading spinner up across full initial render

Three small fixes that together eliminate the visible map jump on app start:

- Mount cc-loading-file-progress-spinner outside the @if (isInitialized())
  block so it appears immediately on page load, not only after files have
  finished loading.
- Skip restoring isLoadingFile and isLoadingMap from persisted state — they
  are runtime-only flags. Restoring a previous session's false value
  briefly hid the spinner mid-boot, causing a show/hide/show flicker.
- Debounce removeLoadingIndicatorAfterRender$ by 350ms so the spinner stays
  visible through the burst of late renders (saved-state blacklist apply,
  then autoFitTo's setTimeout-driven camera jump). Spinner now clears only
  after the map has fully settled.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>