feat(ui): migrate the canonical action-button surface onto <Button>

Sweep the rounded-lg solid/ghost/outline action-button family onto the shared primitive:
ConfirmProvider, ErrorDialog, DownloadDialog, DownloadCenter, downloadModals, downloadAdmin,
ProfileEditor, PersonalViewsModal, SettingsPanel, WatchPage, DraftSaveBar. Deliberately left
on their own styles per the agreed scope: login/onboarding rounded-xl CTAs (Welcome/Onboarding/
Setup/KeyGate), glass Plex surfaces, segmented pills/toggles/switches/chips, dropdown triggers,
data-driven Banner/tone maps, text-xs dense buttons, and tiny inline p-1/p-1.5 icon controls —
none map 1:1 to a variant+size without a visual change, and the repo has no tailwind-merge.

frontend/src/components/ui/DraftSaveBar.tsx

@@ -1,5 +1,6 @@
 import { createPortal } from "react-dom";
 import { Check, RotateCcw, Save } from "lucide-react";
+import { Button } from "./Button";
 
 // The Save / Discard bar shown while an edited draft has unsaved changes (Settings prefs,
 // admin Configuration). Two visual variants share one state machine + markup:
@@ -58,24 +59,27 @@ export function DraftSaveBar({
         )}
       </span>
       <div className="flex items-center gap-2">
-        <button
+        <Button
           data-testid="draft-discard"
+          variant="glass"
+          size="sm"
+          icon={<RotateCcw className="w-4 h-4" />}
           onClick={onDiscard}
           disabled={saving || !dirty}
-          className="glass-card glass-hover flex items-center gap-1.5 px-3 py-1.5 rounded-lg text-sm disabled:opacity-40 transition"
         >
-          <RotateCcw className="w-4 h-4" />
           {labels.discard}
-        </button>
-        <button
+        </Button>
+        <Button
           data-testid="draft-save"
+          variant="primary"
+          size="sm"
+          icon={<Save className="w-4 h-4" />}
           onClick={onSave}
           disabled={saving || !dirty}
-          className="flex items-center gap-1.5 px-3 py-1.5 rounded-lg text-sm btn-primary font-medium shadow-md shadow-accent/20 disabled:opacity-40 transition"
+          className="shadow-md shadow-accent/20"
         >
-          <Save className="w-4 h-4" />
           {saving ? labels.saving : labels.save}
-        </button>
+        </Button>
       </div>
     </div>
   );