feat: live toggle — views re-render when Library Only mode changes

All three explore components now subscribe to exploreSettings:

- explore-view: re-runs the current search when toggled. In
  library-only mode this means instant local-only results; toggling
  off fires the full MB/LB pipeline.

- explore-artist-details: re-runs loadAllData which branches on
  libraryOnly — switching modes live-swaps between the full API
  view and the library-only view.

- explore-album-details: re-renders to pick up any mode-dependent
  display changes.

All subscriptions are cleaned up in disconnectedCallback.

frontend/src/components/explore-view/explore-view.ts

@@ -496,8 +496,23 @@ export class ExploreView extends LitElement {
 
     /* ── Lifecycle ── */
 
+    private unsubSettings?: () => void;
+
+    override connectedCallback() {
+        super.connectedCallback();
+        // Re-render and re-search when library-only mode toggles.
+        this.unsubSettings = exploreSettings.subscribe(() => {
+            this.requestUpdate();
+            // Re-run the current search with the new mode.
+            if (this.searchQuery.trim().length >= MIN_QUERY_LENGTH) {
+                void this.executeSearch();
+            }
+        });
+    }
+
     override disconnectedCallback() {
         super.disconnectedCallback();
+        this.unsubSettings?.();
         if (this.debounceTimer !== null) {
             clearTimeout(this.debounceTimer);
             this.debounceTimer = null;