Fix social/iMessage unfurl metadata (Open Graph + Twitter cards)

- New 1200x630 (1.91:1) og-image.jpg cropped from the 3D stacked-trace hero
- og:image now an ABSOLUTE URL (relative URLs don't unfurl); + og:url,
  og:site_name, og:image:type/width/height/alt
- twitter:card=summary_large_image + twitter title/description/image/alt
- apple-touch-icon.png (180x180) for iMessage/Safari; theme-color; canonical
- Drop orphaned screenshot-hero.jpg (was only the old og:image)

Author: patj

assets/img/apple-touch-icon.png

@@ -5,11 +5,30 @@
   <meta name="viewport" content="width=device-width, initial-scale=1" />
   <title>AetherSDR — A native amateur-radio workstation for FlexRadio</title>
   <meta name="description" content="AetherSDR is a native amateur-radio workstation for FlexRadio 6000, 8000, and Aurora transceivers on Linux, macOS, and Windows. Open interfaces, GPU spectrum, DAX, noise reduction, and the data-mode tools you already use." />
+  <link rel="canonical" href="https://www.aethersdr.com/" />
+  <meta name="theme-color" content="#060b13" />
+
+  <!-- Open Graph -->
+  <meta property="og:type" content="website" />
+  <meta property="og:site_name" content="AetherSDR" />
+  <meta property="og:url" content="https://www.aethersdr.com/" />
   <meta property="og:title" content="AetherSDR — Native. Open. Yours." />
   <meta property="og:description" content="A native amateur-radio workstation for FlexRadio, built around open interfaces and the tools operators already run — WSJT-X, fldigi, JS8Call, VARA, Winlink, and more. Native on Linux, macOS, and Windows." />
-  <meta property="og:type" content="website" />
-  <meta property="og:image" content="assets/img/screenshot-hero.jpg" />
+  <meta property="og:image" content="https://www.aethersdr.com/assets/img/og-image.jpg" />
+  <meta property="og:image:type" content="image/jpeg" />
+  <meta property="og:image:width" content="1200" />
+  <meta property="og:image:height" content="630" />
+  <meta property="og:image:alt" content="AetherSDR's 3D stacked-trace panadapter and waterfall over the 40m band, with the full control surface." />
+
+  <!-- Twitter / X -->
+  <meta name="twitter:card" content="summary_large_image" />
+  <meta name="twitter:title" content="AetherSDR — Native. Open. Yours." />
+  <meta name="twitter:description" content="A native amateur-radio workstation for FlexRadio — open interfaces, GPU spectrum, DAX, and the data-mode tools you already run. Native on Linux, macOS, and Windows." />
+  <meta name="twitter:image" content="https://www.aethersdr.com/assets/img/og-image.jpg" />
+  <meta name="twitter:image:alt" content="AetherSDR's 3D stacked-trace panadapter and waterfall over the 40m band." />
+
   <link rel="icon" type="image/png" href="assets/img/logo-96.png" />
+  <link rel="apple-touch-icon" href="assets/img/apple-touch-icon.png" />
   <link rel="stylesheet" href="styles.css" />
 </head>
 <body>