refactor: replace GlobalSnackbar with sonner toast

Remove the custom 373-line GlobalSnackbar component and its Provider/Hook
in favor of the already-installed sonner library.

Changes:
- Delete src/components/GlobalSnackbar.tsx (+ tests)
- Remove SnackbarProvider from popup/App.tsx and sidepanel/App.tsx
- Replace useSnackbar() calls with toast.success()/toast.error() in:
  - ImageUploader.tsx
  - useQrCode.ts
  - ParsePanel.tsx
  - LiveClock.tsx
- Update test mocks to use sonner instead of GlobalSnackbar

-554 lines, +43 lines (net -511 lines)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/entrypoints/popup/App.tsx

@@ -2,7 +2,6 @@ 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 { getEntryPointType } from '@/config/features';
 import { useMemo } from 'react';
 
@@ -30,14 +29,12 @@ export default function App() {
       visiblePagesKey={routerConfig.visiblePagesKey}
       pageOrderKey={routerConfig.pageOrderKey}
     >
-      <SnackbarProvider initialOptions={{ autoHideDuration: 1500 }}>
-        <div className="app flex flex-col w-[400px] max-w-[400px] min-w-[400px] h-[600px] min-h-[600px] overflow-hidden bg-background sm:w-screen sm:max-w-none sm:min-w-0 sm:h-screen sm:min-h-0">
-          <TopBar />
-          <ErrorBoundary>
-            <RouterContainer />
-          </ErrorBoundary>
-        </div>
-      </SnackbarProvider>
+      <div className="app flex flex-col w-[400px] max-w-[400px] min-w-[400px] h-[600px] min-h-[600px] overflow-hidden bg-background sm:w-screen sm:max-w-none sm:min-w-0 sm:h-screen sm:min-h-0">
+        <TopBar />
+        <ErrorBoundary>
+          <RouterContainer />
+        </ErrorBoundary>
+      </div>
     </RouterProvider>
   );
 }

src/entrypoints/sidepanel/App.tsx

@@ -3,7 +3,6 @@ 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() {
@@ -16,14 +15,12 @@ export default function App() {
 
   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>
+      <div className="app flex flex-col h-screen w-full overflow-hidden">
+        <TopBar />
+        <ErrorBoundary>
+          <RouterContainer />
+        </ErrorBoundary>
+      </div>
     </RouterProvider>
   );
 }