feat(networks): add host/application counts columns and fix Actions header

Adds NetworkWithCounts presentation model and get_networks_with_counts()
server function using a single SQL query with correlated subqueries.
Networks table now shows host count, application count, and has the
Actions column header properly right-aligned to match the Delete button.

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

src/api/networks.rs

@@ -1,9 +1,23 @@
 // api/networks.rs — Server functions for networks
 
 use leptos::prelude::*;
+use serde::{Deserialize, Serialize};
 
 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)]
+pub struct NetworkWithCounts {
+    pub id: i64,
+    pub cidr: String,
+    /// Number of hosts whose IP falls within this network's CIDR range.
+    pub host_count: i64,
+    /// Number of distinct applications linked via ports open on hosts in this network.
+    pub application_count: i64,
+}
+
 // ─── Queries ──────────────────────────────────────────────────────────────────
 
 /// Returns all networks from the database.
@@ -26,6 +40,50 @@ pub async fn get_networks() -> Result<Vec<Network>, ServerFnError> {
         .map_err(|e| ServerFnError::new(e.to_string()))
 }
 
+/// Returns all networks enriched with host and application counts.
+///
+/// A single SQL query fetches everything at once using correlated subqueries,
+/// avoiding N+1 round-trips regardless of the number of networks.
+///
+/// `application_count` = distinct applications whose registered ports appear
+/// among the ports open on hosts in each network (via host_ports → application_ports).
+#[server]
+pub async fn get_networks_with_counts() -> Result<Vec<NetworkWithCounts>, ServerFnError> {
+    use sqlx::{AnyPool, Row};
+
+    let pool = use_context::<AnyPool>()
+        .ok_or_else(|| ServerFnError::new("Database pool not found in context"))?;
+
+    let rows = sqlx::query(
+        "SELECT
+            n.id,
+            n.cidr,
+            (SELECT COUNT(*) FROM hosts WHERE network_id = n.id) AS host_count,
+            (SELECT COUNT(DISTINCT ap.application_id)
+               FROM hosts h
+               JOIN host_ports hp ON hp.host_id = h.id
+               JOIN application_ports ap ON ap.port_number = hp.port_number
+              WHERE h.network_id = n.id) AS application_count
+         FROM networks n
+         ORDER BY n.id",
+    )
+    .fetch_all(&pool)
+    .await
+    .map_err(|e| ServerFnError::new(e.to_string()))?;
+
+    let networks = rows
+        .into_iter()
+        .map(|row| NetworkWithCounts {
+            id:                row.get("id"),
+            cidr:              row.get("cidr"),
+            host_count:        row.get("host_count"),
+            application_count: row.get("application_count"),
+        })
+        .collect();
+
+    Ok(networks)
+}
+
 // ─── Mutations ────────────────────────────────────────────────────────────────
 
 /// Creates a new network with the given CIDR block.