Add loader title hint for SPA navigation feedback

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

app/RSpade/man/spa.txt

@@ -523,6 +523,37 @@ NAVIGATION
             Spa.action.reload();           // Reload current action
             Spa.layout.update_nav();       // Call layout method
 
+    Loader Title Hint:
+        When navigating from a list to a detail page, you can provide a hint
+        for the page title to display while the action loads its data. This
+        provides immediate visual feedback instead of showing a blank or
+        generic title during the loading state.
+
+        Add data-loader-title-hint attribute to links:
+
+            <a href="<%= Rsx.Route('Contacts_View_Action', {id: contact.id}) %>"
+               data-loader-title-hint="<%= contact.name %>">
+              <%= contact.name %>
+            </a>
+
+        When the link is clicked:
+        1. document.title is immediately set to the hint value
+        2. The hint is passed to the action as this.args._loader_title_hint
+        3. Action can use the hint while loading, then replace with real title
+
+        Using the Hint in Actions:
+            async page_title() {
+                // Show hint while loading, real title when data is ready
+                if (this.is_loading() && this.args._loader_title_hint) {
+                    return this.args._loader_title_hint;
+                }
+                return `Contact: ${this.data.contact.name}`;
+            }
+
+        The _loader_title_hint parameter is automatically filtered from URLs
+        generated by Rsx.Route(), so it never appears in the browser address
+        bar or generated links.
+
 SESSION VALIDATION
     After each SPA navigation (except initial load and back/forward), the client
     validates its state against the server by calling Rsx.validate_session().