feat(navigation): link app names on host detail to app detail with back button

- Host detail: application names are now clickable links to
  /applications/:id?back=/hosts/:host_id
- Application detail: back button reads the ?back query param and
  returns to the originating host page (label "← Host") or falls
  back to /applications ("← Applications")

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

src/client/application_detail.rs

@@ -7,7 +7,7 @@
 //   - Delete button  : confirmation modal, then navigates back to /applications
 
 use leptos::prelude::*;
-use leptos_router::hooks::{use_navigate, use_params_map};
+use leptos_router::hooks::{use_navigate, use_params_map, use_query_map};
 
 use crate::api::applications::{
     AddPortToApplication, DeleteApplication, RemovePortFromApplication,
@@ -66,6 +66,16 @@ pub fn ApplicationDetailPage() -> impl IntoView {
             .unwrap_or(0)
     };
 
+    let query = use_query_map();
+    let back_url = move || {
+        query.read().get("back")
+            .map(|s| s.to_string())
+            .unwrap_or_else(|| "/applications".to_string())
+    };
+    let back_label = move || {
+        if back_url().starts_with("/hosts/") { "← Host" } else { "← Applications" }
+    };
+
     let update_action      = ServerAction::<UpdateApplication>::new();
     let add_port_action    = ServerAction::<AddPortToApplication>::new();
     let remove_port_action = ServerAction::<RemovePortFromApplication>::new();
@@ -182,7 +192,9 @@ pub fn ApplicationDetailPage() -> impl IntoView {
                         view! {
                             // ── Page header ───────────────────────────────────
                             <div class="page-header detail-page-header">
-                                <a class="back-btn" href="/applications">"← Applications"</a>
+                                <a class="back-btn" href=move || back_url()>
+                                    {move || back_label()}
+                                </a>
                                 <h1 class="detail-page-title">{move || name_sig.get()}</h1>
                             </div>
 

src/client/host_detail.rs

@@ -385,7 +385,10 @@ pub fn HostDetailPage() -> impl IntoView {
                                         let app_id = app.id;
                                         view! {
                                             <div class="app-row">
-                                                <span class="app-row__name">{app.name}</span>
+                                                <a class="table-link"
+                                                    href=format!("/applications/{}?back=/hosts/{}", app_id, id)>
+                                                    {app.name}
+                                                </a>
                                                 <button
                                                     class="btn-danger"
                                                     type="button"