Fix service widget auto-scroll and remove dead code

Fix service selection scrolling to prevent selector bar from being
hidden by "... X more below" message. When scrolling down, position
selected service one line above the bottom if there's content below,
ensuring the selector remains visible above the overflow message.

Remove unused get_zmq_stats method and service_type field to eliminate
compilation warnings and dead code.

dashboard/src/metrics/store.rs

@@ -86,16 +86,6 @@ impl MetricStore {
         self.current_agent_data.get(hostname)
     }
 
-    /// Get ZMQ communication statistics for a host
-    pub fn get_zmq_stats(&mut self, hostname: &str) -> Option<ZmqStats> {
-        let now = Instant::now();
-        self.zmq_stats.get_mut(hostname).map(|stats| {
-            // Update packet age
-            stats.last_packet_age_secs = now.duration_since(stats.last_packet_time).as_secs_f64();
-            stats.clone()
-        })
-    }
-
     /// Get connected hosts (hosts with recent heartbeats)
     pub fn get_connected_hosts(&self, timeout: Duration) -> Vec<String> {
         let now = Instant::now();