feat(measure): privacy-friendly hit beacon to un-blind GitHub-Pages traffic

Repo traffic API does not count Pages site hits — the more-clickable
awesome-list link points to the live calculator, so live-site clicks were
invisible. Adds a no-cookie, no-PII, no-account beacon (Abacus):
- live: every Pages load
- from-github: arrivals referred by a github.com link (e.g. the merged
  awesome-legal-data entry)
Domain-guarded to ipythoning.github.io so dev/local hits don't pollute.

Author: iPythoning

index.html

@@ -332,5 +332,18 @@ <h3>${s.name}</h3>
     </div>`).join('');
 }
 </script>
+<!-- Privacy-friendly hit beacon: no cookies, no PII, no third-party account.
+     Closes the GitHub-Pages measurement blind spot (repo traffic API does not
+     count Pages hits). `live` = every page load; `from-github` = arrivals whose
+     referrer is a github.com link (e.g. the awesome-legal-data list entry). -->
+<script>
+(function(){
+  if(location.hostname!=='ipythoning.github.io')return;
+  var ns='lien-deadlines-ipy';
+  function hit(k){new Image().src='https://abacus.jasoncameron.dev/hit/'+ns+'/'+k+'?_='+Date.now();}
+  hit('live');
+  if(/(^|\.)github\./i.test(document.referrer))hit('from-github');
+})();
+</script>
 </body>
 </html>