fix(workspace): keep the overlay delay while another playlist refreshes

Refresh preparation skipped the cached-load delay for any playlist, so
opening a cached portal while another playlist prepared a refresh still
flashed the overlay. Only preparation of the shown playlist (any on the
dashboard) now shows it at once.

Also words the J2 layout-shift history from #1895 in the past tense: the
cached-load overlay no longer mounts on a J2 click.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/workspace-shell.md

@@ -195,9 +195,10 @@ services:
 5. `WorkspaceShellCommandPaletteService` owns command-palette dialog lifecycle
    and recent-command recording.
 6. `WorkspaceShellXtreamImportService` owns Xtream import/refresh overlay
-   state and labels. Remote import phases and refresh preparation show the
-   overlay at once. A session that has only read the saved catalog
-   (`loading-cached`, `isImporting` still false) shows it only after
+   state and labels. Remote import phases and refresh preparation of the
+   shown playlist (of any playlist on the dashboard) show the overlay at
+   once. A session that has only read the saved catalog (`loading-cached`,
+   `isImporting` still false) shows it only after
    `XTREAM_LOCAL_LOAD_OVERLAY_DELAY_MS` (300 ms), so a warm open goes from
    the skeleton to the page without flashing the overlay, while a slow or
    stuck cache read still blocks and stays cancellable.