Add disk quota display to services widget

Implement disk quota/total display in services widget showing usage/quota
format. When services don't have specific disk quotas configured, use
system total disk capacity as the quota value.

Changes:
- Add disk_quota_gb field to ServiceData struct in agent
- Add disk_quota_gb field to ServiceInfo struct in dashboard
- Update format_disk_value to show usage/quota format
- Use system disk total capacity as default quota for services
- Rename DiskUsage.total_gb to total_capacity_gb for clarity

Services will now display disk usage as "5.2/500.0 GB" format where
500.0 GB is either the service's specific quota or system total capacity.

agent/src/collectors/service.rs

@@ -113,6 +113,7 @@ impl ServiceCollector {
             cpu_percent,
             sandbox_limit: None, // TODO: Implement sandbox limit detection
             disk_used_gb,
+            disk_quota_gb: 0.0, // Will be set to system total in collect()
             description,
             sub_service: None,
         })
@@ -331,7 +332,7 @@ impl ServiceCollector {
         };
 
         Ok(DiskUsage {
-            total_gb: parse_size(parts[0])?,
+            total_capacity_gb: parse_size(parts[0])?,
             used_gb: parse_size(parts[1])?,
         })
     }
@@ -1122,6 +1123,7 @@ impl Collector for ServiceCollector {
                                     cpu_percent: 0.0,
                                     sandbox_limit: None,
                                     disk_used_gb: 0.0,
+                                    disk_quota_gb: 0.0,
                                     description: None,
                                     sub_service: Some("nginx".to_string()),
                                 });
@@ -1147,6 +1149,7 @@ impl Collector for ServiceCollector {
                                     cpu_percent: 0.0,
                                     sandbox_limit: None,
                                     disk_used_gb: 0.0,
+                                    disk_quota_gb: 0.0,
                                     description: None,
                                     sub_service: Some("docker".to_string()),
                                 });
@@ -1168,6 +1171,7 @@ impl Collector for ServiceCollector {
                         cpu_percent: 0.0,
                         sandbox_limit: None,
                         disk_used_gb: 0.0,
+                        disk_quota_gb: 0.0,
                         description: None,
                         sub_service: None,
                     });
@@ -1176,12 +1180,18 @@ impl Collector for ServiceCollector {
             }
         }
 
-
-        let _disk_usage = self.get_disk_usage().await.unwrap_or(DiskUsage {
-            total_gb: 0.0,
+        let disk_usage = self.get_disk_usage().await.unwrap_or(DiskUsage {
+            total_capacity_gb: 0.0,
             used_gb: 0.0,
         });
 
+        // Set disk quota to system total capacity for services that don't have specific quotas
+        let system_disk_capacity_gb = disk_usage.total_capacity_gb;
+        for service in &mut services {
+            if service.disk_quota_gb == 0.0 {
+                service.disk_quota_gb = system_disk_capacity_gb;
+            }
+        }
         
         // Calculate overall services status
         let services_status = self.determine_services_status(healthy, degraded, failed);
@@ -1226,6 +1236,7 @@ struct ServiceData {
     cpu_percent: f32,
     sandbox_limit: Option<f32>,
     disk_used_gb: f32,
+    disk_quota_gb: f32,
     #[serde(skip_serializing_if = "Option::is_none")]
     description: Option<Vec<String>>,
     #[serde(default)]
@@ -1243,6 +1254,6 @@ enum ServiceStatus {
 
 #[allow(dead_code)]
 struct DiskUsage {
-    total_gb: f32,
+    total_capacity_gb: f32,
     used_gb: f32,
 }