feat(ui): show a tooltip with the full text on truncated titles

Add an `overflowTooltip` Svelte action that sets a native `title` only when
an element is actually clipped (ellipsis or line-clamp), re-checking on
resize. Native title is keyboard/touch reachable and zero-dep, unlike a
hover-only popover. Applied to the clipped titles on MangaCard, BookmarkList,
HistoryList, and the Continue-reading shelf.

Unit tests cover the overflow decision and the set/clear/update behaviour;
an e2e verifies a real-browser truncated card title gets the tooltip while a
short one does not.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/BookmarkList.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
     import { fileUrl } from '$lib/api/client';
     import type { Bookmark } from '$lib/api/bookmarks';
+    import { overflowTooltip } from '$lib/actions/overflowTooltip';
     import BookImage from '@lucide/svelte/icons/book-image';
 
     let {
@@ -34,6 +35,7 @@
                     href="/manga/{b.manga_id}"
                     class="title"
                     data-testid="bookmark-title"
+                    use:overflowTooltip={b.manga_title ?? 'Unknown manga'}
                 >
                     {b.manga_title ?? 'Unknown manga'}
                 </a>