Add VLAN ID display and smart parent assignment for virtual interfaces

Agent changes:
- Parse /proc/net/vlan/config to extract VLAN IDs for interfaces
- Detect primary physical interface via default route
- Auto-assign primary interface as parent for virtual interfaces without explicit parent
- Added vlan_id field to NetworkInterfaceData

Dashboard changes:
- Display VLAN ID in format "interface (vlan X): IP"
- Show VLAN IDs for both nested and standalone virtual interfaces

This ensures virtual interfaces (docker0, tailscale0, etc.) are properly nested
under the primary physical NIC, and VLAN interfaces show their IDs.

Updated to version 0.1.170

dashboard/src/ui/widgets/system.rs

@@ -697,10 +697,19 @@ impl SystemWidget {
                     String::new()
                 };
 
-                let child_text = if !ip_text.is_empty() {
-                    format!("{}: {}", child.name, ip_text)
+                // Format: "name (vlan X): IP" or "name: IP"
+                let child_text = if let Some(vlan_id) = child.vlan_id {
+                    if !ip_text.is_empty() {
+                        format!("{} (vlan {}): {}", child.name, vlan_id, ip_text)
+                    } else {
+                        format!("{} (vlan {}):", child.name, vlan_id)
+                    }
                 } else {
-                    format!("{}:", child.name)
+                    if !ip_text.is_empty() {
+                        format!("{}: {}", child.name, ip_text)
+                    } else {
+                        format!("{}:", child.name)
+                    }
                 };
 
                 lines.push(Line::from(vec![
@@ -724,10 +733,19 @@ impl SystemWidget {
                 String::new()
             };
 
-            let interface_text = if !ip_text.is_empty() {
-                format!("{}: {}", interface.name, ip_text)
+            // Format: "name (vlan X): IP" or "name: IP"
+            let interface_text = if let Some(vlan_id) = interface.vlan_id {
+                if !ip_text.is_empty() {
+                    format!("{} (vlan {}): {}", interface.name, vlan_id, ip_text)
+                } else {
+                    format!("{} (vlan {}):", interface.name, vlan_id)
+                }
             } else {
-                format!("{}:", interface.name)
+                if !ip_text.is_empty() {
+                    format!("{}: {}", interface.name, ip_text)
+                } else {
+                    format!("{}:", interface.name)
+                }
             };
 
             lines.push(Line::from(vec![