chore(seo): mise à jour des URLs pour le nouveau domaine

- Changement de toutes les occurrences de l'ancienne URL vers le nouveau domaine killiandalcin.fr dans les fichiers index.html, robots.txt, sitemap.xml, et les composants Vue.js.
- Mise à jour des métadonnées SEO pour refléter le nouveau domaine dans les pages About, Home, et Projects.
- Commentaire du script de suivi Umami dans index.html pour une future réactivation.

index.html

@@ -9,7 +9,7 @@
   <title>Killian - Full Stack Developer | Vue.js, React, Node.js Expert</title>
   <meta name="title" content="Killian - Full Stack Developer | Vue.js, React, Node.js Expert">
   <meta name="description"
-    content="Professional Full Stack Developer specializing in modern web development with Vue.js, React, Node.js. Expert in Discord bots, web applications, and custom software solutions. Available for freelance projects.">
+    content="Full Stack Developer specializing in Vue.js, React, Node.js. Expert in Discord bots, web apps & custom solutions. Available for freelance.">
   <meta name="keywords"
     content="full stack developer, web developer, Vue.js developer, React developer, Node.js developer, JavaScript developer, Discord bot developer, freelance developer, web development services, custom software solutions">
   <meta name="author" content="Killian">
@@ -19,7 +19,7 @@
 
   <!-- Open Graph / Facebook -->
   <meta property="og:type" content="website">
-  <meta property="og:url" content="https://killian-portfolio.com">
+  <meta property="og:url" content="https://killiandalcin.fr">
   <meta property="og:title" content="Killian - Full Stack Developer | Vue.js, React, Node.js Expert">
   <meta property="og:description"
     content="Professional Full Stack Developer specializing in modern web development. Expert in Discord bots, web applications, and custom solutions.">
@@ -29,14 +29,14 @@
 
   <!-- Twitter -->
   <meta property="twitter:card" content="summary_large_image">
-  <meta property="twitter:url" content="https://killian-portfolio.com">
+  <meta property="twitter:url" content="https://killiandalcin.fr">
   <meta property="twitter:title" content="Killian - Full Stack Developer | Vue.js, React, Node.js Expert">
   <meta property="twitter:description"
     content="Professional Full Stack Developer specializing in modern web development. Expert in Discord bots, web applications, and custom solutions.">
   <meta property="twitter:image" content="/portfolio-preview.jpg">
 
   <!-- Canonical URL -->
-  <link rel="canonical" href="https://killian-portfolio.com">
+  <link rel="canonical" href="https://killiandalcin.fr">
 
   <!-- Favicon -->
   <link rel="icon" href="/favicon.ico">
@@ -60,7 +60,7 @@
     "name": "Killian",
     "jobTitle": "Full Stack Developer",
     "description": "Professional Full Stack Developer specializing in Vue.js, React, Node.js, and modern web technologies",
-    "url": "https://killian-portfolio.com",
+    "url": "https://killiandalcin.fr",
     "sameAs": [
       "https://github.com/killian",
       "https://linkedin.com/in/killian",