Implement nginx site latency monitoring and improve disk usage display

Agent improvements:
- Add reqwest dependency for HTTP latency testing
- Implement measure_site_latency() function for nginx sites
- Add latency_ms field to ServiceData structure
- Measure response times for nginx sites using HEAD requests
- Handle connection failures gracefully with 5-second timeout
- Use HTTPS for external sites, HTTP for localhost

Dashboard improvements:
- Add latency_ms field to ServiceInfo structure
- Display latency for nginx sites: "docker.cmtec.se 134ms"
- Only show latency for nginx sub-services, not other services
- Change disk usage "0" to "<1MB" for better readability

The Services widget now shows:
- Nginx sites with response times when measurable
- Cleaner disk usage formatting for small values
- Improved user experience with meaningful latency data

dashboard/src/data/metrics.rs

@@ -128,6 +128,8 @@ pub struct ServiceInfo {
     pub description: Option<Vec<String>>,
     #[serde(default)]
     pub sub_service: Option<String>,
+    #[serde(default)]
+    pub latency_ms: Option<f32>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]

dashboard/src/ui/services.rs

@@ -105,12 +105,23 @@ fn render_metrics(
         };
         
         if svc.sub_service.is_some() {
-            // Sub-services only show name and status, no memory/CPU/disk/sandbox data
+            // Sub-services (nginx sites) only show name and status, no memory/CPU/disk data
+            // Add latency information for nginx sites if available
+            let service_name_with_latency = if let Some(parent) = &svc.sub_service {
+                if parent == "nginx" && svc.latency_ms.is_some() {
+                    format!("{} {:.0}ms", svc.name, svc.latency_ms.unwrap())
+                } else {
+                    svc.name.clone()
+                }
+            } else {
+                svc.name.clone()
+            };
+            
             data.add_row_with_sub_service(
                 Some(WidgetStatus::new(status_level)),
                 description,
                 vec![
-                    svc.name.clone(),
+                    service_name_with_latency,
                     "".to_string(),
                     "".to_string(),
                     "".to_string(),
@@ -139,7 +150,7 @@ fn render_metrics(
 
 fn format_bytes(mb: f32) -> String {
     if mb < 0.1 {
-        "0".to_string()
+        "<1MB".to_string()
     } else if mb < 1.0 {
         format!("{:.0}kB", mb * 1000.0)
     } else if mb < 1000.0 {