fix: close previous EventSource before starting new sync job

Prevents output from a previous run bleeding into the next panel when
two sync operations are triggered in quick succession.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

webui.py

@@ -385,7 +385,9 @@ async function refreshStats() {
   } catch(e) {}
 }
 
+let _activeSrc = null;
 async function doSync(endpoint, label) {
+  if (_activeSrc) { _activeSrc.close(); _activeSrc = null; }
   const btn = event.currentTarget;
   btn.disabled = true;
   const r = await fetch(endpoint, {method:'POST'});
@@ -400,6 +402,7 @@ async function doSync(endpoint, label) {
   panel.style.display = 'block';
   panel.innerHTML = '<div class="ln">' + label + '…</div>';
   const src = new EventSource('/stream/' + d.job_id);
+  _activeSrc = src;
   src.onmessage = e => {
     const ev = JSON.parse(e.data);
     if (ev.type === 'done') {
@@ -409,6 +412,7 @@ async function doSync(endpoint, label) {
       panel.appendChild(div);
       panel.scrollTop = panel.scrollHeight;
       src.close();
+      _activeSrc = null;
       btn.disabled = false;
       refreshStats();
       return;