Fix og:image & twitter:image to use branded social preview; add twitter:site

- og:image and twitter:image now point to clawbio-social-preview.png in ClawBio/ClawBio instead of the org avatar
- Added twitter:site meta tag (@manuelcorpas)
- Fixes the weak LinkedIn/Twitter preview card that was showing just a plain white avatar image

Author: manuelcorpas

index.html

@@ -9,12 +9,13 @@
   <meta property="og:site_name" content="ClawBio">
   <meta property="og:title" content="🦖 ClawBio — Bioinformatics AI Agent Skills">
   <meta property="og:description" content="ClawBio is the first bioinformatics-native AI agent skill library. Run GWAS, phylogenetics, proteomics and more — local-first, privacy-focused, and fully reproducible. Built on OpenClaw.">
-  <meta property="og:image" content="https://avatars.githubusercontent.com/u/264498536?v=4">
+  <meta property="og:image" content="https://raw.githubusercontent.com/ClawBio/ClawBio/main/img/clawbio-social-preview.png">
   <meta property="og:url" content="https://clawbio.github.io">
   <meta name="twitter:card" content="summary_large_image">
+  <meta name="twitter:site" content="@manuelcorpas">
   <meta name="twitter:title" content="🦖 ClawBio — Bioinformatics AI Agent Skills">
   <meta name="twitter:description" content="ClawBio is the first bioinformatics-native AI agent skill library. Run GWAS, phylogenetics, proteomics and more — local-first, privacy-focused, and fully reproducible. Built on OpenClaw.">
-  <meta name="twitter:image" content="https://avatars.githubusercontent.com/u/264498536?v=4">
+  <meta name="twitter:image" content="https://raw.githubusercontent.com/ClawBio/ClawBio/main/img/clawbio-social-preview.png">
   <style>
     *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
     :root {