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/pages/Base64Converter/index.tsx

@@ -0,0 +1,43 @@
+import { useI18n } from '@/utils/chromeI18n';
+import { useStorageState } from '@/utils/useStorageState';
+import type { Base64ConverterPageMode } from '@/types/storage';
+import TextMode from './TextMode';
+import Base64ConverterSection from './Base64ConverterSection';
+import SwitchButtonGroup from '@/components/SwitchButtonGroup';
+
+const VALID_PAGE_MODES: readonly Base64ConverterPageMode[] = ['text', 'file', 'image'];
+const isValidPageMode = (val: unknown): val is Base64ConverterPageMode =>
+  typeof val === 'string' && (VALID_PAGE_MODES as readonly string[]).includes(val);
+
+type PageMode = Base64ConverterPageMode;
+
+export default function Index() {
+  const { t } = useI18n('base64Converter');
+  const [pageMode, setPageMode] = useStorageState(
+    'base64Converter/pageMode',
+    'text',
+    isValidPageMode,
+  );
+
+  return (
+    <div className="p-4 w-full flex flex-col space-y-4 min-h-[520px] select-none">
+      <SwitchButtonGroup
+        value={pageMode}
+        options={[
+          { value: 'text', label: t('base64Converter:textMode') },
+          { value: 'file', label: t('base64Converter:fileMode') },
+          { value: 'image', label: t('base64Converter:imageMode') },
+        ]}
+        onChange={(value: PageMode) => setPageMode(value)}
+        size="small"
+        className="w-full sm:w-auto"
+      />
+
+      <div className="w-full pt-1">
+        {pageMode === 'text' && <TextMode onSwitchToImageMode={() => setPageMode('image')} />}
+        {pageMode === 'file' && <Base64ConverterSection mode="file" />}
+        {pageMode === 'image' && <Base64ConverterSection mode="image" />}
+      </div>
+    </div>
+  );
+}