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

site/src/layouts/Base.astro

@@ -338,6 +338,11 @@ try {
             <div id="zip-label">Drop your Strava export .zip<br/>or click to browse</div>
             <input id="zip-input" type="file" accept=".zip" class="hidden" />
           </div>
+          <label class="flex items-center gap-2 mt-3 text-xs text-zinc-400 cursor-pointer select-none">
+            <input id="zip-private" type="checkbox" class="accent-blue-500" />
+            Mark all imported activities as private
+            <span class="text-zinc-600">(Strava export doesn't include privacy settings)</span>
+          </label>
           <p id="zip-status" class="mt-3 text-xs text-center leading-relaxed" style="min-height: 1.25rem"></p>
         </div>
       </div>
@@ -447,6 +452,7 @@ try {
       const zipInput      = document.getElementById('zip-input');
       const zipLabel      = document.getElementById('zip-label');
       const zipStatus     = document.getElementById('zip-status');
+      const zipPrivate    = document.getElementById('zip-private');
       const drop              = document.getElementById('upload-drop');
       const input             = document.getElementById('upload-input');
       const label             = document.getElementById('upload-label');
@@ -690,6 +696,7 @@ try {
 
         const fd = new FormData();
         fd.append('file', file);
+        fd.append('private', zipPrivate?.checked ? 'true' : 'false');
 
         // POST the file; server responds with SSE stream immediately after receiving body
         const xhr = new XMLHttpRequest();