fix(notifications): use the success level for success toasts

The 'Synced N playlists' and 'View link copied' toasts used the default info level,
which renders in the accent colour and read as an error/alert. Mark them level:success
so they show the green check — clearly positive and theme-independent.

frontend/src/components/Playlists.tsx

@@ -172,7 +172,7 @@ export default function Playlists() {
       const r = await api.syncYoutubePlaylists();
       qc.invalidateQueries({ queryKey: ["playlists"] });
       qc.invalidateQueries({ queryKey: ["playlist"] });
-      notify({ message: t("playlists.syncedToast", { count: r.synced }) });
+      notify({ level: "success", message: t("playlists.syncedToast", { count: r.synced }) });
     } catch {
       notify({ level: "warning", message: t("playlists.syncFailed") });
     } finally {

frontend/src/components/Sidebar.tsx

@@ -202,7 +202,7 @@ export default function Sidebar({
   async function shareView() {
     try {
       await navigator.clipboard.writeText(shareUrl(filters));
-      notify({ message: t("sidebar.shareCopied") });
+      notify({ level: "success", message: t("sidebar.shareCopied") });
     } catch {
       notify({ level: "warning", message: t("sidebar.shareFailed") });
     }