refactor(heartbeat): add configurable interval and channel-aware routing

feat(config): add heartbeat interval configuration with default 30 minutes

feat(state): migrate state file from workspace root to state directory

feat(channels): skip internal channels in outbound dispatcher

feat(agent): record last active channel for heartbeat context

refactor(subagent): use configurable default model instead of provider default

pkg/channels/manager.go

@@ -218,6 +218,9 @@ func (m *Manager) StopAll(ctx context.Context) error {
 func (m *Manager) dispatchOutbound(ctx context.Context) {
 	logger.InfoC("channels", "Outbound dispatcher started")
 
+	// Internal channels that don't have actual handlers
+	internalChannels := map[string]bool{"cli": true, "system": true, "subagent": true}
+
 	for {
 		select {
 		case <-ctx.Done():
@@ -229,6 +232,11 @@ func (m *Manager) dispatchOutbound(ctx context.Context) {
 				continue
 			}
 
+			// Silently skip internal channels
+			if internalChannels[msg.Channel] {
+				continue
+			}
+
 			m.mu.RLock()
 			channel, exists := m.channels[msg.Channel]
 			m.mu.RUnlock()