fix(navigation): back button on host detail returns to application when coming from there

- application_detail: host links now include ?back=/applications/:id
- host_detail: back_label handles /applications/ prefix → "← Application"

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

src/client/application_detail.rs

@@ -178,7 +178,7 @@ pub fn ApplicationDetailPage() -> impl IntoView {
                                         view! {
                                             <div class="app-row">
                                                 <a class="table-link"
-                                                    href=format!("/hosts/{}", host.id)>
+                                                    href=format!("/hosts/{}?back=/applications/{}", host.id, id)>
                                                     {host.name}
                                                 </a>
                                                 <span class="cell-mono">{host.ip}</span>

src/client/host_detail.rs

@@ -232,7 +232,9 @@ pub fn HostDetailPage() -> impl IntoView {
             .unwrap_or_else(|| "/hosts".to_string())
     };
     let back_label = move || {
-        if back_url().starts_with("/networks/") { "← Network" } else { "← Hosts" }
+        if back_url().starts_with("/networks/")     { "← Network" }
+        else if back_url().starts_with("/applications/") { "← Application" }
+        else { "← Hosts" }
     };
 
     let update_action      = ServerAction::<UpdateHost>::new();