feat: add language switcher between English and German

- Add language toggle button in header (EN/DE)
- Link directly to the other language version
- Style consistent with existing header buttons
- Accessible with proper aria-labels

src/index.html

@@ -20,7 +20,10 @@
 					<img src="./bowl.png" width="40" alt="CODE CRISPIES Logo" />
 					<h1>CODE<span>CRISPIES</span></h1>
 				</div>
-				<button id="help-btn" class="help-toggle" aria-label="Help">?</button>
+				<div class="header-actions">
+					<a href="./index.de.html" class="lang-switch" aria-label="Sprache wechseln: Deutsch">DE</a>
+					<button id="help-btn" class="help-toggle" aria-label="Help">?</button>
+				</div>
 			</header>
 
 			<!-- Main Game Layout -->