feat(cards): leech detection in /me/stats + Stats-Page-Sektion

Karten mit ≥4 Lapses werden im Stats-Endpoint als `leech_cards`
geliefert (mit Front-Snippet, Deck-Name, Lapses-Count, sortiert
desc, max 20). Stats-Page zeigt eine rote „Schwierige Karten"-
Sektion mit Link in den Card-Editor.

* apps/api/src/routes/me.ts: GROUP BY card → SUM(lapses) ≥ 4
  Filter, frontSnippetFor()-Helper für alle 6 Card-Types
  (basic, basic-reverse, cloze, image-occlusion, audio-front,
  typing, multiple-choice). Cloze-Markup wird gestrippt damit
  der Snippet UI-tauglich ist.
* apps/web Stats-Page: neue CardSurface mit Warning-Icon, scrollbare
  Liste mit Front + Deck + Lapses-Badge, Empty-State.
* i18n in DE/EN/FR/IT/ES (5 Strings + plural-Form).

104/104 Tests grün (kein neuer Test — bestehende /me/stats-Tests
covern die Aggregations-Form), web check 0 errors.

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

apps/web/src/lib/api/me.ts

@@ -40,6 +40,17 @@ export function deleteMe() {
 	return api<DeleteMeResult>('/api/v1/me/delete', { method: 'POST' });
 }
 
+export interface LeechCard {
+	card_id: string;
+	deck_id: string;
+	deck_name: string;
+	type: string;
+	front_snippet: string;
+	lapses: number;
+	reps: number;
+	last_review: string | null;
+}
+
 export interface UserStats {
 	user_id: string;
 	generated_at: string;
@@ -55,6 +66,8 @@ export interface UserStats {
 	retention_reps: number;
 	retention_lapses: number;
 	due_forecast: { day: string; n: number }[];
+	leech_threshold: number;
+	leech_cards: LeechCard[];
 }
 
 export function loadStats() {

apps/web/src/lib/i18n/de.ts

@@ -310,6 +310,11 @@ export const de: TranslationNode = {
 		forecast_title: 'Nächste 7 Tage',
 		forecast_desc: 'Fällige Karten je Tag.',
 		forecast_empty: 'Nichts fällig.',
+		leeches_title: 'Schwierige Karten',
+		leeches_desc: 'Karten mit {threshold}+ Ausrutschern — Kandidaten zum Umformulieren oder Aufteilen.',
+		leeches_none: 'Keine zähen Karten — sauber.',
+		leeches_lapses: '{n} Ausrutscher',
+		leeches_lapses_one: '{n} Ausrutscher',
 		loading: 'Lade…',
 		error: 'Fehler: {msg}',
 	},

apps/web/src/lib/i18n/en.ts

@@ -305,6 +305,11 @@ export const en: TranslationNode = {
 		forecast_title: 'Next 7 days',
 		forecast_desc: 'Cards due per day.',
 		forecast_empty: 'Nothing scheduled.',
+		leeches_title: 'Tough cards',
+		leeches_desc: 'Cards with {threshold}+ lapses — candidates to reword or split.',
+		leeches_none: 'No leeches — clean slate.',
+		leeches_lapses: '{n} lapses',
+		leeches_lapses_one: '{n} lapse',
 		loading: 'Loading…',
 		error: 'Error: {msg}',
 	},

apps/web/src/lib/i18n/es.ts

@@ -305,6 +305,11 @@ export const es: TranslationNode = {
 		forecast_title: 'Próximos 7 días',
 		forecast_desc: 'Tarjetas pendientes por día.',
 		forecast_empty: 'Nada programado.',
+		leeches_title: 'Cartas difíciles',
+		leeches_desc: 'Cartas con {threshold}+ olvidos — candidatas para reformular o dividir.',
+		leeches_none: 'Ninguna carta difícil — todo bien.',
+		leeches_lapses: '{n} olvidos',
+		leeches_lapses_one: '{n} olvido',
 		loading: 'Cargando…',
 		error: 'Error: {msg}',
 	},

apps/web/src/lib/i18n/fr.ts

@@ -305,6 +305,11 @@ export const fr: TranslationNode = {
 		forecast_title: '7 prochains jours',
 		forecast_desc: 'Cartes à réviser par jour.',
 		forecast_empty: 'Rien de prévu.',
+		leeches_title: 'Cartes coriaces',
+		leeches_desc: 'Cartes avec {threshold}+ oublis — à reformuler ou diviser.',
+		leeches_none: 'Aucune carte difficile — tout va bien.',
+		leeches_lapses: '{n} oublis',
+		leeches_lapses_one: '{n} oubli',
 		loading: 'Chargement…',
 		error: 'Erreur : {msg}',
 	},

apps/web/src/lib/i18n/it.ts

@@ -305,6 +305,11 @@ export const it: TranslationNode = {
 		forecast_title: 'Prossimi 7 giorni',
 		forecast_desc: 'Carte da ripassare per giorno.',
 		forecast_empty: 'Niente in programma.',
+		leeches_title: 'Carte ostiche',
+		leeches_desc: 'Carte con {threshold}+ ricadute — da riformulare o dividere.',
+		leeches_none: 'Nessuna carta difficile — pulito.',
+		leeches_lapses: '{n} ricadute',
+		leeches_lapses_one: '{n} ricaduta',
 		loading: 'Caricamento…',
 		error: 'Errore: {msg}',
 	},

apps/web/src/routes/stats/+page.svelte

@@ -7,7 +7,7 @@
 	import { apiErrorMessage } from '$lib/api/error.ts';
 	import { stackLayers } from '$lib/utils/deck-tilt';
 	import CardSurface from '$lib/components/CardSurface.svelte';
-	import { ChartBar, Fire, Brain, CalendarDots, Target, CalendarCheck } from '@mana/shared-icons';
+	import { ChartBar, Fire, Brain, CalendarDots, Target, CalendarCheck, Warning } from '@mana/shared-icons';
 
 	let stats   = $state<UserStats | null>(null);
 	let loading = $state(true);
@@ -19,6 +19,7 @@
 	const actGridLayers      = stackLayers('stats-act-grid', 3);
 	const retentionLayers    = stackLayers('stats-retention', 3);
 	const forecastLayers     = stackLayers('stats-forecast', 3);
+	const leechesLayers      = stackLayers('stats-leeches', 3);
 
 	const peakDay = $derived.by(() => {
 		if (!stats) return 1;
@@ -310,6 +311,42 @@
 		</CardSurface>
 	</li>
 
+	<!-- Schwierige Karten (Leeches) -->
+	<li class="stack-wrap">
+		{#each leechesLayers as layer, i (i)}
+			<div class="layer" style:transform="translate({layer.dx}px,{layer.dy}px) rotate({layer.tilt}deg)" aria-hidden="true"></div>
+		{/each}
+		<CardSurface size="md" colorAccent="#DC2626">
+			<div class="card-inner">
+				<div class="card-corner">
+					<Warning size={24} weight="duotone" aria-hidden="true" />
+				</div>
+				<div class="card-body">
+					<p class="card-title">{t('stats.leeches_title')}</p>
+					<p class="card-desc">{t('stats.leeches_desc', { threshold: stats!.leech_threshold })}</p>
+					{#if stats!.leech_cards.length === 0}
+						<p class="retention-none">{t('stats.leeches_none')}</p>
+					{:else}
+						<ul class="leech-list">
+							{#each stats!.leech_cards as leech (leech.card_id)}
+								<li class="leech-item">
+									<a class="leech-link" href={`/cards/${leech.card_id}/edit`}>
+										<span class="leech-front">{leech.front_snippet || '—'}</span>
+										<span class="leech-meta">
+											<span class="leech-deck">{leech.deck_name}</span>
+											<span class="leech-sep">·</span>
+											<span class="leech-lapses">{t('stats.leeches_lapses', { n: leech.lapses })}</span>
+										</span>
+									</a>
+								</li>
+							{/each}
+						</ul>
+					{/if}
+				</div>
+			</div>
+		</CardSurface>
+	</li>
+
 </ul>
 {/if}
 
@@ -539,4 +576,55 @@
 	.act-cell.level-2 { background: #10B981; opacity: 0.5; }
 	.act-cell.level-3 { background: #10B981; opacity: 0.75; }
 	.act-cell.level-4 { background: #10B981; }
+
+	.leech-list {
+		list-style: none;
+		margin: 0.5rem 0 0;
+		padding: 0;
+		display: flex;
+		flex-direction: column;
+		gap: 0.375rem;
+		max-height: 14rem;
+		overflow-y: auto;
+	}
+
+	.leech-item { margin: 0; }
+
+	.leech-link {
+		display: flex;
+		flex-direction: column;
+		gap: 0.125rem;
+		padding: 0.5rem 0.625rem;
+		border-radius: 0.375rem;
+		text-decoration: none;
+		color: inherit;
+		background: hsl(var(--color-muted) / 0.4);
+		transition: background 120ms;
+	}
+
+	.leech-link:hover,
+	.leech-link:focus-visible {
+		background: hsl(var(--color-muted));
+		outline: 2px solid #DC2626;
+		outline-offset: -2px;
+	}
+
+	.leech-front {
+		font-size: 0.875rem;
+		font-weight: 500;
+		white-space: nowrap;
+		overflow: hidden;
+		text-overflow: ellipsis;
+	}
+
+	.leech-meta {
+		font-size: 0.75rem;
+		color: hsl(var(--color-muted-foreground));
+		display: flex;
+		gap: 0.375rem;
+		align-items: center;
+	}
+
+	.leech-sep { opacity: 0.5; }
+	.leech-lapses { color: #DC2626; font-weight: 500; }
 </style>