feat(portal): add light/dark theme sync and OA drive navigation

Unify chat and OA drive appearance with shared memind-theme storage, default light mode, and cross-frame sync so users can switch themes from chat or the drive shell.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/App.tsx

@@ -91,6 +91,7 @@ function AuthenticatedApp({
             }
           : undefined
       }
+      onOpenOaDrive={user ? () => navigate('/space/oa/drive') : undefined}
       onOpenPage={user ? (pageId) => navigate(`/space/page/${pageId}`) : undefined}
       onOpenAdmin={
         user?.role === 'admin'
@@ -121,6 +122,7 @@ function AuthenticatedApp({
           element={<FeedbackRoutes user={user} onLogout={handleLogout} />}
         />
         <Route path="/health" element={<Navigate to="/" replace />} />
+        <Route path="/oa-drive" element={<Navigate to="/space/oa/drive" replace />} />
         <Route path="/" element={chatElement} />
         <Route path="*" element={<Navigate to="/" replace />} />
       </Routes>