fix(seo): add admin UI for social media URLs

Addresses reviewer feedback: social media fields (Facebook, Twitter/X, Instagram, YouTube) were added to the backend and frontend interfaces but had no admin UI for station owners to configure them.

Added a 'Social Media' section to the station config form with four URL inputs that persist via the existing station-config API.

src/app/admin/admin-station-form.component.html

@@ -184,6 +184,31 @@
         </div>
       </div>
 
+      <!-- Social Media -->
+      <div class="form-section">
+        <h3>Social Media</h3>
+        <div class="form-group">
+          <label for="social_facebook">Facebook URL</label>
+          <input id="social_facebook" type="url" [(ngModel)]="social_facebook" name="social_facebook"
+                 placeholder="https://facebook.com/yourstation">
+        </div>
+        <div class="form-group">
+          <label for="social_twitter">Twitter / X URL</label>
+          <input id="social_twitter" type="url" [(ngModel)]="social_twitter" name="social_twitter"
+                 placeholder="https://x.com/yourstation">
+        </div>
+        <div class="form-group">
+          <label for="social_instagram">Instagram URL</label>
+          <input id="social_instagram" type="url" [(ngModel)]="social_instagram" name="social_instagram"
+                 placeholder="https://instagram.com/yourstation">
+        </div>
+        <div class="form-group">
+          <label for="social_youtube">YouTube URL</label>
+          <input id="social_youtube" type="url" [(ngModel)]="social_youtube" name="social_youtube"
+                 placeholder="https://youtube.com/@yourstation">
+        </div>
+      </div>
+
       <!-- Page Content -->
       <div class="form-section">
         <h3>Page Content</h3>