Develop (#55)

feat: optimize dashboard/search UX and simplify extension architecture

Redesign Dashboard with compact tool grid and recently used tools
Improve TopBar search UX with Cmd/Ctrl+K shortcut and better history navigation
Reorganize project structure into src/
Migrate i18n from react-i18next to chrome.i18n
Remove runtime language switch and settings page
Remove HTML/Markdown conversion tools
Clean up unused code, dead animations, redundant comments, and imports
Improve component consistency with shadcn/ui patterns
Replace hardcoded strings/colors with i18n tokens and theme tokens
Add comprehensive project documentation and coding standards
Fix CI artifact upload workflow and multiple TypeScript/test issues

Includes various refactors, UI polish, i18n cleanup, CI improvements,
and maintenance updates across the codebase.

src/entrypoints/sidepanel/App.tsx

@@ -0,0 +1,29 @@
+import { useEffect } from 'react';
+import RouterProvider from '@/providers/RouterProvider';
+import TopBar from '@/components/TopBar';
+import RouterContainer from '@/components/RouterContainer';
+import ErrorBoundary from '@/components/ErrorBoundary';
+import { SnackbarProvider } from '@/components/GlobalSnackbar';
+import { MessageAction, sendMessage } from '@/utils/messages';
+
+export default function App() {
+  useEffect(() => {
+    sendMessage(MessageAction.SIDE_PANEL_STATE_CHANGED, { isOpen: true });
+    return () => {
+      sendMessage(MessageAction.SIDE_PANEL_STATE_CHANGED, { isOpen: false });
+    };
+  }, []);
+
+  return (
+    <RouterProvider defaultRoute="dashboard" syncKey="app/sidepanelRoute">
+      <SnackbarProvider initialOptions={{ autoHideDuration: 1500 }}>
+        <div className="app flex flex-col h-screen w-full overflow-hidden">
+          <TopBar />
+          <ErrorBoundary>
+            <RouterContainer />
+          </ErrorBoundary>
+        </div>
+      </SnackbarProvider>
+    </RouterProvider>
+  );
+}