Add spinner on connect/disconnect

static/panel.css

@@ -283,6 +283,13 @@ svg { width: 22px; height: 22px; fill: currentColor; }
 .spotify:disabled { opacity: .5; }
 /* The account playing on this room right now. */
 .spotify[aria-pressed="true"] { border: 2px solid var(--ink); }
+/* While a resume or disconnect is on its way, the logo turns into a
+   spinner. Swapped by a class for the same reason as the transport icons.
+   It ticks round in eight steps, like Font Awesome's own fa-spin-pulse. */
+.spotify .spinner { display: none; }
+.spotify.loading .brand { display: none; }
+.spotify.loading .spinner { display: block; animation: spin 1s steps(8) infinite; }
+@keyframes spin { to { transform: rotate(360deg); } }
 
 /* --- source card ------------------------------------------------------ */
 .source-button {