Fix favicon reference and add main landmark for accessibility

- Update Layout.astro to use favicon.ico instead of non-existent favicon.svg
- Add main landmark wrapper to index.astro to fix Lighthouse accessibility error

Author: GreenFlux

src/layouts/Layout.astro

@@ -18,7 +18,7 @@ const canonicalUrl = new URL(Astro.url.pathname, Astro.site || 'https://greenflu
     <meta charset="UTF-8" />
     <meta name="description" content={description} />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+    <link rel="icon" type="image/x-icon" href="/favicon.ico" />
     <link rel="canonical" href={canonicalUrl} />
     <title>{title}</title>
 

src/pages/index.astro

@@ -11,10 +11,12 @@ import Footer from '../components/Footer.astro';
 <Layout title="GreenFlux Portfolio">
   <div id="scroll-progress"></div>
   <Navigation />
-  <Hero />
-  <Portfolio />
-  <About />
-  <Social />
+  <main>
+    <Hero />
+    <Portfolio />
+    <About />
+    <Social />
+  </main>
   <Footer />
 
   <script>