feat: human-friendly session titles in header and sidebar

Replace raw session keys/UUIDs with readable names derived from
session metadata (label, kind, channel). Priority: label > kind-based
name (Main, Cron, Task) with channel suffix > cleaned key fallback.

New utility: src/lib/sessionName.ts used by both Header and Sidebar.

src/lib/sessionName.ts

@@ -0,0 +1,49 @@
+import type { Session } from '../types';
+
+/**
+ * Derive a human-friendly display name for a session.
+ *
+ * Priority:
+ * 1. label (if set, e.g. sub-agent labels)
+ * 2. "Main" for kind=main
+ * 3. Kind + channel (e.g. "Cron · telegram")
+ * 4. Channel name capitalized
+ * 5. Cleaned session key (strip agent:xxx: prefix, truncate UUIDs)
+ */
+export function sessionDisplayName(session: Session): string {
+  if (session.label) return session.label;
+
+  const kind = session.kind;
+  const channel = session.channel;
+
+  if (kind === 'main') {
+    return channel ? `Main · ${capitalize(channel)}` : 'Main';
+  }
+
+  if (kind === 'cron') {
+    return channel ? `Cron · ${capitalize(channel)}` : 'Cron';
+  }
+
+  if (kind === 'isolated') {
+    return channel ? `Task · ${capitalize(channel)}` : 'Task';
+  }
+
+  if (channel) return capitalize(channel);
+
+  // Fallback: clean the session key
+  return cleanSessionKey(session.key);
+}
+
+function capitalize(s: string): string {
+  return s.charAt(0).toUpperCase() + s.slice(1);
+}
+
+function cleanSessionKey(key: string): string {
+  // Strip "agent:<id>:" prefix
+  const stripped = key.replace(/^agent:[^:]+:/, '');
+  // If it looks like a UUID, show first 8 chars
+  if (/^[0-9a-f]{8}-[0-9a-f]{4}-/.test(stripped)) {
+    return stripped.slice(0, 8) + '…';
+  }
+  return stripped;
+}