Summarize LiveTrack sessions and prune stale ones

Fetching a session's track now also grabs its summary (name, activity
type, distance, duration) from the same page and stores it — sessions
the panel has actually shown replace their raw UUID with that summary,
and are kept indefinitely regardless of age. A session nobody ever
opened (no summary) is more likely test/dead data than something worth
keeping, so it's dropped automatically after 48h.

public/css/style.css

@@ -471,13 +471,16 @@ html, body {
   cursor: wait;
 }
 
-.livetrack-panel__id {
-  font-family: monospace;
+.livetrack-panel__label {
   overflow: hidden;
   text-overflow: ellipsis;
   white-space: nowrap;
 }
 
+.livetrack-panel__label--id {
+  font-family: monospace;
+}
+
 .livetrack-panel__time {
   flex-shrink: 0;
   color: #888;