Display session duration in sidebar and simplify date formatting

Show human-readable session duration (e.g. "23m", "1h 15m") in the
session list metadata row when duration > 0. Add formatSessionDuration
helper that handles sub-minute, minute-only, and hour+minute ranges.

Also replace try/catch in formatDate with an isNaN guard on the parsed
Date, which is more idiomatic and avoids swallowing unrelated errors.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/client/components/SessionList.tsx

@@ -96,6 +96,12 @@ export function SessionList({ sessions, loading, selectedId, onSelect }: Props)
                   <span>{formatDate(session.modified || session.created)}</span>
                   <span className="text-border">·</span>
                   <span className="tabular-nums">{session.messageCount} msgs</span>
+                  {session.duration && session.duration > 0 && (
+                    <>
+                      <span className="text-border">·</span>
+                      <span className="tabular-nums">{formatSessionDuration(session.duration)}</span>
+                    </>
+                  )}
                 </div>
               </button>
             );
@@ -154,17 +160,24 @@ function formatProjectName(project: string): string {
   return project;
 }
 
+function formatSessionDuration(ms: number): string {
+  const minutes = Math.floor(ms / 60000);
+  if (minutes < 1) return "<1m";
+  if (minutes < 60) return `${minutes}m`;
+  const hours = Math.floor(minutes / 60);
+  const rem = minutes % 60;
+  if (rem === 0) return `${hours}h`;
+  return `${hours}h ${rem}m`;
+}
+
 function formatDate(dateStr: string): string {
   if (!dateStr) return "";
-  try {
   const d = new Date(dateStr);
+  if (isNaN(d.getTime())) return dateStr;
   return d.toLocaleDateString(undefined, {
     month: "short",
     day: "numeric",
     hour: "2-digit",
     minute: "2-digit",
   });
-  } catch {
-    return dateStr;
-  }
 }