feat: [US-052] - Activity history sidebar

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/editor/Toolbar.tsx

@@ -15,6 +15,7 @@ type ToolbarProps = {
   onImport: () => void
   onProjectSettings: () => void
   onShare: () => void
+  onHistory: () => void
   connectionState?: ConnectionState
   presenceUsers?: PresenceUser[]
 }
@@ -44,6 +45,7 @@ export default function Toolbar({
   onImport,
   onProjectSettings,
   onShare,
+  onHistory,
   connectionState,
   presenceUsers,
 }: ToolbarProps) {
@@ -108,6 +110,12 @@ export default function Toolbar({
         >
           Share
         </button>
+        <button
+          onClick={onHistory}
+          className="rounded border border-zinc-300 bg-white px-3 py-1.5 text-sm font-medium text-zinc-700 hover:bg-zinc-50 focus:outline-none focus:ring-2 focus:ring-blue-500 focus:ring-offset-2 dark:border-zinc-600 dark:bg-zinc-700 dark:text-zinc-200 dark:hover:bg-zinc-600 dark:focus:ring-offset-zinc-800"
+        >
+          History
+        </button>
         <button
           onClick={onSave}
           disabled={isSaving}