feat(AppHeader): improve ad display logic and responsiveness

- Enhanced the AppHeader component to support separate ad slots for mobile and desktop views, improving ad display based on viewport width.
- Introduced a responsive design that adjusts ad dimensions and formats for better visibility across different screen sizes.
- Updated methods to dynamically determine the active ad slot and handle viewport resizing events for optimal ad rendering.

frontend/src/components/AppHeader.vue

@@ -10,12 +10,20 @@
       </div>
       <div class="header-ad" v-if="showHeaderAd">
         <ins
+          v-if="isMobileAd"
+          key="header-ad-mobile"
           class="adsbygoogle"
-          style="display:block"
+          style="display:inline-block;width:320px;height:50px"
           data-ad-client="ca-pub-1104166651501135"
-          :data-ad-slot="adSlotId"
-          data-ad-format="horizontal"
-          data-full-width-responsive="false"
+          :data-ad-slot="activeAdSlotId"
+        ></ins>
+        <ins
+          v-else
+          key="header-ad-desktop"
+          class="adsbygoogle"
+          style="display:inline-block;width:728px;height:90px"
+          data-ad-client="ca-pub-1104166651501135"
+          :data-ad-slot="activeAdSlotId"
         ></ins>
       </div>
       <div class="header-meta">
@@ -60,6 +68,7 @@ export default {
   data() {
     return {
       adInitialized: false,
+      viewportWidth: typeof window !== 'undefined' ? window.innerWidth : 1280,
       /** Endonyme: jede Sprache bezeichnet sich in ihrer eigenen Sprache. */
       uiLocaleOptions: [
         { value: 'de', nativeLabel: 'Deutsch' },
@@ -89,7 +98,7 @@ export default {
       };
     },
     showHeaderAd() {
-      if (!this.adSlotId) {
+      if (!this.activeAdSlotId) {
         return false;
       }
       const path = this.$route?.path || '';
@@ -103,9 +112,27 @@ export default {
         path.startsWith('/falukant/home')
       );
     },
-    adSlotId() {
-      const slot = String(import.meta.env.VITE_ADSENSE_HEADER_SLOT || '').trim();
+    desktopAdSlotId() {
+      const slot = String(
+        import.meta.env.VITE_ADSENSE_HEADER_SLOT_DESKTOP
+        || import.meta.env.VITE_ADSENSE_HEADER_SLOT
+        || ''
+      ).trim();
       return /^\d{6,}$/.test(slot) ? slot : '';
+    },
+    mobileAdSlotId() {
+      const slot = String(
+        import.meta.env.VITE_ADSENSE_HEADER_SLOT_MOBILE
+        || import.meta.env.VITE_ADSENSE_HEADER_SLOT
+        || ''
+      ).trim();
+      return /^\d{6,}$/.test(slot) ? slot : '';
+    },
+    isMobileAd() {
+      return this.viewportWidth < 960;
+    },
+    activeAdSlotId() {
+      return this.isMobileAd ? this.mobileAdSlotId : this.desktopAdSlotId;
     }
   },
   watch: {
@@ -116,9 +143,30 @@ export default {
           this.$nextTick(() => this.initHeaderAd());
         }
       }
+    },
+    isMobileAd(next, prev) {
+      if (next !== prev) {
+        this.adInitialized = false;
+        if (this.showHeaderAd) {
+          this.$nextTick(() => this.initHeaderAd());
+        }
+      }
+    }
+  },
+  mounted() {
+    if (typeof window !== 'undefined') {
+      window.addEventListener('resize', this.handleResize, { passive: true });
+    }
+  },
+  beforeUnmount() {
+    if (typeof window !== 'undefined') {
+      window.removeEventListener('resize', this.handleResize);
     }
   },
   methods: {
+    handleResize() {
+      this.viewportWidth = window.innerWidth;
+    },
     initHeaderAd() {
       if (!this.showHeaderAd) return;
       if (this.adInitialized) return;
@@ -252,28 +300,26 @@ export default {
 }
 
 .header-ad {
-  flex: 1 1 260px;
-  min-width: 180px;
-  max-width: 560px;
-  min-height: 54px;
-  max-height: 54px;
+  flex: 1 1 728px;
+  min-width: 320px;
+  max-width: 728px;
+  min-height: 90px;
+  max-height: 90px;
   display: flex;
   align-items: center;
+  justify-content: center;
   overflow: hidden;
 }
 
 .header-ad .adsbygoogle {
-  width: 100% !important;
-  height: 54px !important;
-  min-height: 54px !important;
-  max-height: 54px !important;
+  width: 100%;
+  max-width: 100%;
   overflow: hidden !important;
 }
 
 .header-ad :deep(iframe),
 .header-ad :deep([id^="aswift_"]) {
-  height: 54px !important;
-  max-height: 54px !important;
+  max-width: 100% !important;
 }
 
 .header-meta__context {
@@ -407,22 +453,26 @@ export default {
   .header-ad {
     order: 3;
     width: 100%;
-    max-width: none;
+    max-width: 320px;
     flex: 1 1 100%;
-    min-height: 44px;
-    max-height: 44px;
+    min-height: 50px;
+    max-height: 50px;
   }
 
   .header-ad .adsbygoogle {
-    height: 44px !important;
-    min-height: 44px !important;
-    max-height: 44px !important;
+    width: 320px !important;
+    min-width: 320px !important;
+    max-width: 320px !important;
+    height: 50px !important;
+    min-height: 50px !important;
+    max-height: 50px !important;
   }
 
   .header-ad :deep(iframe),
   .header-ad :deep([id^="aswift_"]) {
-    height: 44px !important;
-    max-height: 44px !important;
+    width: 320px !important;
+    height: 50px !important;
+    max-height: 50px !important;
   }
 
   .header-meta {