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/ContinueReadingShelf.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
     import { fileUrl } from '$lib/api/client';
     import { chapterLabel } from '$lib/api/chapters';
+    import { overflowTooltip } from '$lib/actions/overflowTooltip';
     import type { ReadProgressSummary } from '$lib/api/read_progress';
     import BookImage from '@lucide/svelte/icons/book-image';
 
@@ -66,7 +67,7 @@
                             </span>
                         {/if}
                     </span>
-                    <span class="title" data-testid="continue-title-{p.manga_id}">{p.manga_title}</span>
+                    <span class="title" data-testid="continue-title-{p.manga_id}" use:overflowTooltip={p.manga_title}>{p.manga_title}</span>
                     <span class="target">{targetLabel(p)}</span>
                 </a>
             </li>