feat(frontend): mobile account hub + library wrapper (0.60.0)

Phase 5 (final) of the mobile redesign: /profile/account becomes an
inset-grouped iOS-style hub on mobile and the new /library route hosts
a SegmentedControl over Bookmarks / Collections / History. Profile-
layout horizontal tabs hide below 640px. Desktop layout is unchanged.

- New /library/+page.ts loads bookmarks, collections, and read-history
  in parallel so segmented-control tabs swap instantly without a new
  round trip. 401 → unauthenticated path with sign-in prompt.
- New /library/+page.svelte renders the SegmentedControl with ?tab=
  as the source of truth. Bookmarks reuses the existing BookmarkList,
  Collections reuses CollectionsGrid, History inlines a slim cover +
  title + "Continue Ch. N" row list. `goto(..., { replaceState: true })`
  drives the URL — plain `replaceState` from $app/navigation doesn't
  reliably re-trigger $page-derived state.
- BottomNav's Library tab now points at /library (Phase 1 placeholder
  was /bookmarks). The Phase 1 mobile-chrome spec is updated to expect
  the new target and mocks the additional library data endpoints.
- /profile/+layout.svelte hides the horizontal tabs below 640px — the
  bottom-nav Library/Account tabs plus the account hub carry mobile
  cross-section navigation.
- /profile/account/+page.svelte gains a mobile hub: a centered avatar
  + username + "Member since" header, a row group with Profile /
  Preferences / Change password rows (the last opening a bottom
  Sheet hosting the existing password form snippet), and a separate
  group with a red "Log out" row that reuses the layout's logout
  flow (logout API → session.setUser(null) → preferences.clearForLogout
  → goto('/login')). Desktop keeps the inline card with the form.
- matchMedia gates the hub vs. desktop card so the password form
  testids never duplicate on the page — the snippet is rendered in
  exactly one mount at a time.
- 9 Playwright tests cover the Library nav handoff, segmented-control
  sub-tab swap with URL, sign-in CTAs on both routes, account hub
  composition, password sheet open flow, logout flow (POST /auth/
  logout + redirect to /login), profile tabs hiding on mobile, and
  the desktop regression where the inline card is the only password
  surface.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/routes/+layout.svelte

@@ -39,6 +39,7 @@
         '/upload': 'Mangalord | Upload',
         '/bookmarks': 'Mangalord | Bookmarks',
         '/collections': 'Mangalord | Collections',
+        '/library': 'Mangalord | Library',
         '/profile': 'Mangalord | Profile',
         '/profile/account': 'Mangalord | Account',
         '/profile/bookmarks': 'Mangalord | Bookmarks',
@@ -53,19 +54,21 @@
 
     const layoutTitle = $derived(STATIC_TITLES[$page.route?.id ?? ''] ?? 'Mangalord');
 
-    // Mobile bottom-nav tabs. Library consolidates Bookmarks / Collections /
-    // History — it currently links to /bookmarks as the closest existing
-    // route; Phase 5 introduces /library with internal segmented sub-tabs
-    // and this href flips at that point. Browse temporarily shares Home's
-    // destination until the curated-feed split lands.
+    // Mobile bottom-nav tabs. Library is now its own wrapper at /library
+    // (Phase 5) hosting a SegmentedControl over Bookmarks / Collections /
+    // History; the older top-level /bookmarks + /collections routes stay
+    // active for desktop users and as deep-link targets, so they remain
+    // in the `match` set. Browse temporarily shares Home's destination
+    // until the curated-feed split lands.
     const MOBILE_TABS: BottomNavTab[] = [
         { label: 'Home', href: '/', icon: House, match: [] },
         { label: 'Browse', href: '/', icon: Search, match: [] },
         {
             label: 'Library',
-            href: '/bookmarks',
+            href: '/library',
             icon: BookOpen,
             match: [
+                '/library',
                 '/bookmarks',
                 '/collections',
                 '/profile/bookmarks',