feat: add session indicators and top exec commands to dashboard

Add visual indicators to session tables (replay badge when events exist,
exec badge for exec sessions) and a new "Top Exec Commands" table on the
dashboard. Includes EventCount field on Session, GetTopExecCommands on
Store interface, and truncateCommand template function.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/storage/memstore.go

@@ -336,12 +336,20 @@ func (m *MemoryStore) GetRecentSessions(_ context.Context, limit int, activeOnly
 	m.mu.Lock()
 	defer m.mu.Unlock()
 
+	// Count events per session.
+	eventCounts := make(map[string]int)
+	for _, e := range m.SessionEvents {
+		eventCounts[e.SessionID]++
+	}
+
 	var sessions []Session
 	for _, s := range m.Sessions {
 		if activeOnly && s.DisconnectedAt != nil {
 			continue
 		}
-		sessions = append(sessions, *s)
+		sess := *s
+		sess.EventCount = eventCounts[s.ID]
+		sessions = append(sessions, sess)
 	}
 	sort.Slice(sessions, func(i, j int) bool {
 		return sessions[i].ConnectedAt.After(sessions[j].ConnectedAt)
@@ -352,6 +360,30 @@ func (m *MemoryStore) GetRecentSessions(_ context.Context, limit int, activeOnly
 	return sessions, nil
 }
 
+func (m *MemoryStore) GetTopExecCommands(_ context.Context, limit int) ([]TopEntry, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	counts := make(map[string]int64)
+	for _, s := range m.Sessions {
+		if s.ExecCommand != nil {
+			counts[*s.ExecCommand]++
+		}
+	}
+
+	entries := make([]TopEntry, 0, len(counts))
+	for k, v := range counts {
+		entries = append(entries, TopEntry{Value: k, Count: v})
+	}
+	sort.Slice(entries, func(i, j int) bool {
+		return entries[i].Count > entries[j].Count
+	})
+	if limit > 0 && len(entries) > limit {
+		entries = entries[:limit]
+	}
+	return entries, nil
+}
+
 func (m *MemoryStore) CloseActiveSessions(_ context.Context, disconnectedAt time.Time) (int64, error) {
 	m.mu.Lock()
 	defer m.mu.Unlock()