feat(profile): add a desktop Page-tags section

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>

backend/Cargo.lock

@@ -1517,7 +1517,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.88.0"
+version = "0.89.0"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.88.0"
+version = "0.89.0"
 edition = "2021"
 default-run = "mangalord"