fix(study): Hint-Text entfernt, kein vertikales Scrollen

- grade-hint Paragraph und CSS entfernt (Keyboard-Shortcuts sichtbar
  in den Buttons selbst via kbd-Tags)
- min-height: 100vh → height: 100vh + overflow: hidden

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/routes/study/[deckId]/+page.svelte

@@ -253,8 +253,6 @@
 				</button>
 			</div>
 		{/if}
-
-		<p class="grade-hint">{t('study_session.grade_hint')}</p>
 	{/if}
 	</div>
 </div>
@@ -266,7 +264,8 @@
 		flex-direction: column;
 		align-items: center;
 		justify-content: center;
-		min-height: 100vh;
+		height: 100vh;
+		overflow: hidden;
 		padding: 2rem 1.5rem;
 	}
 
@@ -581,11 +580,4 @@
 	.grade.grade-easy:hover:not(:disabled) {
 		background: hsl(var(--color-success) / 0.08);
 	}
-
-	.grade-hint {
-		margin: 1.25rem 0 0;
-		text-align: center;
-		font-size: 0.75rem;
-		color: hsl(var(--color-muted-foreground));
-	}
 </style>