fix(seo): add missing sitemap locale entries, swap KoalaSearching→RemoteProf on alternatives index

- Add 39 missing language-specific sitemap entries for fr/es/it/.../uk
  alternatives pages (index, teleparty, screen-sharing)
- Replace KoalaSearching image with RemoteProf (professor koala)
  on the Guides & Comparisons overview page
- Update og:image, twitter:image, and img src accordingly

website/alternatives/index.html

@@ -34,13 +34,13 @@
     <meta property="og:url" content="https://sync.koalastuff.net/{{LANG_PREFIX}}alternatives">
     <meta property="og:title" content="{{ALT_INDEX_TITLE}}">
     <meta property="og:description" content="{{ALT_INDEX_META_DESC}}">
-    <meta property="og:image" content="https://sync.koalastuff.net/assets/KoalaSearching.webp">
+    <meta property="og:image" content="https://sync.koalastuff.net/assets/RemoteProf.webp">
 
     <!-- Twitter / X -->
     <meta name="twitter:card" content="summary_large_image">
     <meta name="twitter:title" content="{{ALT_INDEX_TITLE}}">
     <meta name="twitter:description" content="{{ALT_INDEX_META_DESC}}">
-    <meta name="twitter:image" content="https://sync.koalastuff.net/assets/KoalaSearching.webp">
+    <meta name="twitter:image" content="https://sync.koalastuff.net/assets/RemoteProf.webp">
 
     <!-- Structured Data (Schema.org) for Breadcrumbs -->
     <script type="application/ld+json">
@@ -121,7 +121,7 @@
     <main class="legal-content">
         <div class="legal-card" data-reveal style="padding: 2.5rem 2rem;">
             <div style="display: flex; justify-content: center;">
-                <img src="{{ASSET_PATH}}assets/KoalaSearching.webp" alt="Koala using magnifying glass" class="legal-mascot" width="180" height="180">
+                <img src="{{ASSET_PATH}}assets/RemoteProf.webp" alt="Koala teaching and explaining concepts" class="legal-mascot" width="180" height="180">
             </div>
             
             <h1>