Page tags were a first-class section of the mobile Library tab but had no
home in the desktop /profile tabs, so desktop users couldn't browse their
tagged pages without going through /search. Add a /profile/page-tags route
that reuses PageTagsList (the same component the mobile Library renders) and
a "Page tags" tab between Collections and History.
The loader mirrors the library wrapper's page-tags fetch; 401 → sign-in
prompt, matching the other profile sub-routes.
e2e: the desktop Page-tags tab navigates to /profile/page-tags and renders
the list.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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