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/library/+page.ts

@@ -0,0 +1,44 @@
+import { ApiError } from '$lib/api/client';
+import { listMyBookmarks } from '$lib/api/bookmarks';
+import { listMyCollections } from '$lib/api/collections';
+import { listMyReadProgress } from '$lib/api/read_progress';
+import type { PageLoad } from './$types';
+
+export const ssr = false;
+
+/**
+ * Loads bookmarks + collections + reading-history in one shot so the
+ * Library segmented control can swap between sub-tabs without firing a
+ * second round trip per tap. 401 → unauthenticated path; the page
+ * surfaces a sign-in prompt and renders empty lists.
+ */
+export const load: PageLoad = async () => {
+    const empty = {
+        authenticated: true,
+        bookmarks: [] as Awaited<ReturnType<typeof listMyBookmarks>>['items'],
+        collections: [] as Awaited<ReturnType<typeof listMyCollections>>['items'],
+        history: [] as Awaited<ReturnType<typeof listMyReadProgress>>['items'],
+        error: null as string | null
+    };
+    try {
+        const [bookmarks, collections, history] = await Promise.all([
+            listMyBookmarks(),
+            listMyCollections({ limit: 200 }),
+            listMyReadProgress({ limit: 100 })
+        ]);
+        return {
+            ...empty,
+            bookmarks: bookmarks.items,
+            collections: collections.items,
+            history: history.items
+        };
+    } catch (e) {
+        if (e instanceof ApiError && e.status === 401) {
+            return { ...empty, authenticated: false };
+        }
+        if (e instanceof ApiError) {
+            return { ...empty, error: e.message };
+        }
+        throw e;
+    }
+};