feat(04-03): add Daten section with Export/Import/Reset buttons in parent area

- HTML section with export-btn, import-btn, reset-btn, hidden file input
- CSS styles for action buttons including danger variant for reset

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

index.html

@@ -166,6 +166,19 @@
 						</div>
 					</section>
 
+					<section class="parent__section">
+						<h2>Daten</h2>
+						<div class="parent__data-actions">
+							<button class="parent__action-btn" id="export-btn">Fortschritt exportieren</button>
+							<div class="parent__import-row">
+								<button class="parent__action-btn" id="import-btn">Fortschritt importieren</button>
+								<input type="file" id="import-file" accept=".json" style="display:none">
+							</div>
+							<button class="parent__action-btn parent__action-btn--danger" id="reset-btn">Alles zuruecksetzen</button>
+						</div>
+						<p class="parent__data-info" id="data-feedback" style="display:none"></p>
+					</section>
+
 				</div>
 			</div>
 		</section>