feat(networks): add network detail page with paginated host list and contextual back button

- API: add get_network(id) server function
- NetworkDetailPage at /networks/:id — network name + CIDR header, paginated
  host table (Name, IP, Ports, Apps) linking to /hosts/:id?back=/networks/:id
- Networks list: make network name a link to its detail page
- HostDetailPage: read ?back= query param to show "← Network" or "← Hosts"
  and navigate to the correct destination

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

style/rust-ipam.css

@@ -1207,3 +1207,19 @@ td.col-actions {
   justify-content: flex-end;
   margin-top: var(--size-lg);
 }
+
+/* ============================================================
+   NETWORK DETAIL PAGE
+   ============================================================ */
+
+.network-detail-page {
+  max-width: 720px;
+}
+
+/* CIDR displayed below the network name in the header */
+.network-detail-cidr {
+  font-family: var(--font-mono);
+  font-size: var(--font-sm);
+  color: var(--text-secondary);
+  margin: 0;
+}