option to keep all activities private from strava zip, fix copy of register link

site/src/pages/invites/index.astro

@@ -47,6 +47,17 @@ import Base from '../../layouts/Base.astro';
     return li;
   }
 
+  function fallbackCopy(text: string, done: () => void) {
+    const ta = document.createElement('textarea');
+    ta.value = text;
+    ta.style.cssText = 'position:fixed;opacity:0;top:0;left:0';
+    document.body.appendChild(ta);
+    ta.focus();
+    ta.select();
+    try { document.execCommand('copy'); done(); } catch (_) {}
+    document.body.removeChild(ta);
+  }
+
   async function loadInvites() {
     try {
       const r = await fetch('/api/invites', { credentials: 'include' });
@@ -66,9 +77,16 @@ import Base from '../../layouts/Base.astro';
       // Copy link buttons
       listEl.querySelectorAll('.copy-btn').forEach(btn => {
         btn.addEventListener('click', () => {
-          navigator.clipboard.writeText((btn as HTMLElement).dataset.link ?? '');
-          btn.textContent = 'Copied!';
-          setTimeout(() => { btn.textContent = 'Copy link'; }, 2000);
+          const text = (btn as HTMLElement).dataset.link ?? '';
+          const done = () => {
+            btn.textContent = 'Copied!';
+            setTimeout(() => { btn.textContent = 'Copy link'; }, 2000);
+          };
+          if (navigator.clipboard) {
+            navigator.clipboard.writeText(text).then(done).catch(() => fallbackCopy(text, done));
+          } else {
+            fallbackCopy(text, done);
+          }
         });
       });
     } catch (e: any) {