fix: the spinner by the path takes room only while busy, opening and closing smoothly

internal/server/web/templates/files.html

@@ -23,16 +23,18 @@
   .fm-bar .fm-pathbox .btn.sq { position:absolute; right:4px; top:4px; width:26px; height:26px; border:1px solid transparent; }
   .fm-bar .fm-pathbox .btn.sq:hover { border-color:var(--border); background:#151a21; }
   .spinner { width:16px; height:16px; border:2px solid var(--border); border-top-color:var(--accent);
-             border-radius:50%; animation:spin .7s linear infinite; display:inline-block; flex:none; visibility:hidden; }
+             border-radius:50%; animation:spin .7s linear infinite; display:inline-block; flex:none; }
   @keyframes spin { to { transform:rotate(360deg); } }
   /* Busy indicator; while files upload it also shows how far they got, and a
-     click on it lists them. It holds its place, hidden or not, so the path
-     field beside it never jumps. */
-  #uppct:not(:empty) { min-width:9.5ch; }
+     click on it lists them. It takes room only while it shows. */
   #uppct:empty { display:none; }
-  .fm-bar .busy { margin:0 -3px; }
-  .busy { flex:none; min-width:16px; justify-content:center; display:inline-flex; align-items:center; gap:6px; background:none; border:0; padding:0;
+  .busy { flex:none; display:none; align-items:center; gap:8px; background:none; border:0; padding:0 2px;
           height:34px; color:var(--muted); font-size:13px; font-variant-numeric:tabular-nums; cursor:default; }
+  /* Folded to nothing when idle (the negative margin takes back the bar's
+     gap), it opens smoothly, and only for work that lasts a moment. */
+  .fm-bar .busy { display:inline-flex; box-sizing:border-box; max-width:0; padding:0; margin-left:-8px; opacity:0;
+                  overflow:hidden; white-space:nowrap; transition:max-width .3s ease, margin-left .3s ease, opacity .25s ease; }
+  .fm-bar .busy.on { max-width:120px; margin-left:0; opacity:1; transition-delay:.15s; }
   .busy:hover { background:none; }
   .busy.up { cursor:pointer; color:var(--text); }
   .busy.up:hover { color:var(--accent); }
@@ -343,8 +345,7 @@
 (function () {
   const agentID = {{.Agent.ID}};
   let busyN = 0;
-  // The spinner keeps its place when hidden, so the path field never jumps.
-  function setBusy(on) { busyN += on ? 1 : -1; if (busyN < 0) busyN = 0; document.getElementById('spin').style.visibility = busyN > 0 ? 'visible' : 'hidden'; }
+  function setBusy(on) { busyN += on ? 1 : -1; if (busyN < 0) busyN = 0; document.getElementById('busy').classList.toggle('on', busyN > 0); }
   const api = (op, body) => {
     setBusy(true);
     return fetch('/api/panel/agents/' + encodeURIComponent(agentID) + '/fs/' + op, {