feat(networks): add delete confirmation modal with host count warning

Show a modal before deleting a network. If the network has hosts,
display a warning with the exact count since they will be cascade-deleted.
Host count comes from the existing NetworkWithCounts data (no extra query).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/api/networks.rs

@@ -8,7 +8,7 @@ use crate::models::Network;
 // Network row augmented with pre-computed counts.
 // Defined here (not in models.rs) because it is a presentation model
 // specific to the Networks page, not a pure domain entity.
-#[derive(Clone, Debug, Serialize, Deserialize)]
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
 pub struct NetworkWithCounts {
     pub id: i64,
     pub cidr: String,