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/e2e/overflow-tooltip.spec.ts

@@ -0,0 +1,66 @@
+import { test, expect, type Page } from './fixtures';
+
+// The overflowTooltip action sets a native `title` on a manga card's title
+// only when it's actually truncated. Verified in a real browser (jsdom can't
+// lay out, so scrollWidth/clientWidth are meaningless there).
+
+const LONG_TITLE =
+    'An Extraordinarily Long Manga Title That Cannot Possibly Fit Within Two Clamped Lines Of A Narrow Card';
+const SHORT_TITLE = 'Bleach';
+
+function manga(id: string, title: string) {
+    return {
+        id,
+        title,
+        status: 'ongoing',
+        alt_titles: [],
+        description: null,
+        cover_image_path: null,
+        created_at: '2026-01-01T00:00:00Z',
+        updated_at: '2026-01-01T00:00:00Z',
+        authors: [],
+        genres: []
+    };
+}
+
+async function mockHome(page: Page) {
+    await page.route('**/api/v1/auth/config', (r) =>
+        r.fulfill({ status: 200, contentType: 'application/json', body: JSON.stringify({ self_register_enabled: true, private_mode: false }) })
+    );
+    await page.route('**/api/v1/auth/me', (r) =>
+        r.fulfill({ status: 401, contentType: 'application/json', body: JSON.stringify({ error: { code: 'unauthenticated', message: 'no' } }) })
+    );
+    await page.route('**/api/v1/auth/me/preferences', (r) =>
+        r.fulfill({ status: 401, contentType: 'application/json', body: '{}' })
+    );
+    await page.route('**/api/v1/genres*', (r) =>
+        r.fulfill({ status: 200, contentType: 'application/json', body: '[]' })
+    );
+    await page.route('**/api/v1/me/read-progress*', (r) =>
+        r.fulfill({ status: 401, contentType: 'application/json', body: JSON.stringify({ error: { code: 'unauthenticated', message: 'no' } }) })
+    );
+    await page.route('**/api/v1/mangas*', (r) =>
+        r.fulfill({
+            status: 200,
+            contentType: 'application/json',
+            body: JSON.stringify({
+                items: [manga('m1', LONG_TITLE), manga('m2', SHORT_TITLE)],
+                page: { limit: 50, offset: 0, total: 2 }
+            })
+        })
+    );
+}
+
+test('adds a title tooltip to truncated card titles but not to ones that fit', async ({ page }) => {
+    await mockHome(page);
+    // Narrow (mobile) grid so the long title clamps and overflows.
+    await page.setViewportSize({ width: 390, height: 844 });
+    await page.goto('/');
+
+    const longLink = page.getByRole('link', { name: LONG_TITLE });
+    await expect(longLink).toBeVisible();
+    await expect(longLink).toHaveAttribute('title', LONG_TITLE);
+
+    const shortLink = page.getByRole('link', { name: SHORT_TITLE });
+    await expect(shortLink).not.toHaveAttribute('title');
+});