[refactor](trx-frontend-http): consolidate to single auth interface

Remove duplicate logout button from About tab. Use only the header
Login/Logout button for unified authentication control.

The About tab now shows the authentication badge (when logged in)
without the redundant logout button.

Single login view:
- Auth gate with Login form + Continue as Guest button (when no rx pass)
- Header Login/Logout button for quick access
- Auth badge in About tab showing current role

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -90,13 +90,11 @@ function showAuthError(msg) {
 }
 
 function updateAuthUI() {
-  const btn = document.getElementById("logout-btn");
   const badge = document.getElementById("auth-badge");
   const badgeRole = document.getElementById("auth-role-badge");
   const headerAuthBtn = document.getElementById("header-auth-btn");
 
   if (authRole) {
-    btn.style.display = "block";
     badge.style.display = "block";
     badgeRole.textContent = authRole === "control" ? "Control (full access)" : "RX (read-only)";
     if (headerAuthBtn) {
@@ -104,7 +102,6 @@ function updateAuthUI() {
       headerAuthBtn.style.display = "block";
     }
   } else {
-    btn.style.display = "none";
     badge.style.display = "none";
     if (headerAuthBtn) {
       headerAuthBtn.textContent = "Login";
@@ -1276,13 +1273,6 @@ if (guestBtn) {
   });
 }
 
-// Setup logout button
-document.getElementById("logout-btn").addEventListener("click", async () => {
-  if (confirm("Are you sure you want to logout?")) {
-    await authLogout();
-  }
-});
-
 // Setup header auth button (Login/Logout)
 const headerAuthBtn = document.getElementById("header-auth-btn");
 if (headerAuthBtn) {

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -239,10 +239,7 @@
       </div>
     </div>
     <div id="tab-about" class="tab-panel" style="display:none;">
-      <div style="margin-bottom: 1rem;">
-        <button id="logout-btn" type="button" style="display:none; padding: 0.5rem 1rem; background: var(--accent-red, #ff6b6b); color: var(--bg-primary); border: none; border-radius: 0.25rem; font-weight: 600; cursor: pointer;">Logout</button>
-        <div id="auth-badge" style="display:none; margin-top: 0.5rem; color: var(--text-muted); font-size: 0.85rem;">Authenticated as: <strong id="auth-role-badge">--</strong></div>
-      </div>
+      <div id="auth-badge" style="display:none; margin-bottom: 1rem; padding: 0.5rem; background: var(--bg-secondary); border-radius: 0.25rem; color: var(--text-muted); font-size: 0.85rem;">Authenticated as: <strong id="auth-role-badge">--</strong></div>
       <table class="about-table">
         <tr><td>Server version</td><td id="about-server-ver">--</td></tr>
         <tr><td>Server address</td><td id="about-server-addr">--</td></tr>