fix(mobile): restore response-viewer eye button on phones

The header-right tray (02fa3f3) was reworked into a position:fixed
collapsible panel with a hamburger toggle, but the toggle button, its
JS, and CSS were later reverted on master while the container kept a
static `mobile-collapsed` class. With no expand mechanism left, the
header-right stayed display:none on mobile, so the response-viewer eye
icon was unreachable even with "Response Viewer" enabled — desktop was
fine because the media-query rule doesn't apply there.

Restore the simple inline always-visible header-right layout (dev's
known-good state). The showResponseViewer setting still controls the
eye's --hidden marker class.

Verified on iPhone viewport: eye visible (26x26) with setting on, hidden
with setting off, tap opens the viewer; desktop eye unaffected.

src/web/public/index.html

@@ -81,7 +81,7 @@
       <!-- Detached single-session window title (shown only in solo mode) -->
       <div class="solo-session-title" id="soloSessionTitle" style="display: none;" aria-live="polite"></div>
 
-      <div class="header-right mobile-collapsed" id="headerRight">
+      <div class="header-right" id="headerRight">
         <button class="btn-icon-header btn-solo-redock" id="soloRedockBtn" style="display: none;" onclick="window.close()" title="Re-dock to dashboard (close window)" aria-label="Re-dock session to dashboard">&#x229E;</button>
         <button class="tunnel-indicator" id="tunnelIndicator" style="display: none;" onclick="app.toggleTunnelPanel()" title="Cloudflare Tunnel" aria-label="Tunnel status">
           <span class="tunnel-dot"></span>