refactor: enhance live stream layout with loading state and caching

- Added `XtreamCachedContentScope` type to manage content loading states.
- Updated live stream layout to show a loading skeleton when content is being fetched.
- Introduced styles for loading content in the live stream layout.
- Enhanced unit tests to cover loading states and caching behavior.
- Modified `XtreamWorkspaceRouteSession` to handle cached content loading and state management.
- Improved handling of optional connection values in playlist data.
- Updated workspace context panel to reflect import states and loading conditions.

Entire-Checkpoint: c2cea9c530e6

docs/architecture/workspace-shell.md

@@ -54,7 +54,12 @@ Provider route integration:
 3. Xtream and Stalker parent routes attach route-scoped session providers that
    bootstrap the active playlist, sync provider section state, and clean up
    provider-local state when the route is destroyed.
-4. Workspace routes no longer rely on nested provider shell components for
+4. Xtream route bootstrap is DB-first for already imported Electron playlists:
+   if the requested section has persisted categories and content, the route
+   hydrates from SQLite even when the portal status probe reports unavailable,
+   expired, or inactive. Fresh/no-cache Xtream routes still use the status probe
+   to block remote imports before the loading overlay starts.
+5. Workspace routes no longer rely on nested provider shell components for
    hidden local chrome.
 
 ## Shell Structure