feat(ui): toggle to hide the response-viewer (eye) header button

The eye button (View last response) was the only header control with
no visibility setting. Add App Settings -> Display -> "Response
Viewer" (showResponseViewer, default on, per-device like the other
header toggles; added to the displayKeys no-cross-device-sync set
along with showLifecycleLog, which was missing from it).

Hiding uses a marker class with higher specificity — the base rule is
display:inline-flex !important, so an inline style cannot override it.

Verified via Playwright on a fresh instance: 8/8 — default visible,
hides live on save, persists across reload, server schema accepts the
key, re-enable restores, mobile storage isolated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/web/public/index.html

@@ -985,6 +985,13 @@
                   <span class="slider"></span>
                 </label>
               </div>
+              <div class="settings-item" title="Show the response viewer (eye) button in header">
+                <span class="settings-item-label">Response Viewer</span>
+                <label class="switch switch-sm">
+                  <input type="checkbox" id="appSettingsShowResponseViewer">
+                  <span class="slider"></span>
+                </label>
+              </div>
               <div class="settings-item" title="Show the multi-monitor button in the header (opens Codeman spanned across all displays)">
                 <span class="settings-item-label">Multi-monitor Button</span>
                 <label class="switch switch-sm">

src/web/public/settings-ui.js

@@ -308,6 +308,7 @@ Object.assign(CodemanApp.prototype, {
     document.getElementById('appSettingsShowTokenCount').checked = settings.showTokenCount ?? defaults.showTokenCount ?? true;
     document.getElementById('appSettingsShowCost').checked = settings.showCost ?? defaults.showCost ?? false;
     document.getElementById('appSettingsShowLifecycleLog').checked = settings.showLifecycleLog ?? defaults.showLifecycleLog ?? true;
+    document.getElementById('appSettingsShowResponseViewer').checked = settings.showResponseViewer ?? defaults.showResponseViewer ?? true;
     document.getElementById('appSettingsShowMonitor').checked = settings.showMonitor ?? defaults.showMonitor ?? false;
     document.getElementById('appSettingsShowProjectInsights').checked = settings.showProjectInsights ?? defaults.showProjectInsights ?? false;
     document.getElementById('appSettingsShowFileBrowser').checked = settings.showFileBrowser ?? defaults.showFileBrowser ?? false;
@@ -1323,6 +1324,7 @@ Object.assign(CodemanApp.prototype, {
       showTokenCount: document.getElementById('appSettingsShowTokenCount').checked,
       showCost: document.getElementById('appSettingsShowCost').checked,
       showLifecycleLog: document.getElementById('appSettingsShowLifecycleLog').checked,
+      showResponseViewer: document.getElementById('appSettingsShowResponseViewer').checked,
       showMonitor: document.getElementById('appSettingsShowMonitor').checked,
       showProjectInsights: document.getElementById('appSettingsShowProjectInsights').checked,
       showFileBrowser: document.getElementById('appSettingsShowFileBrowser').checked,
@@ -1670,6 +1672,14 @@ Object.assign(CodemanApp.prototype, {
       lifecycleBtn.style.display = showLifecycleLog ? '' : 'none';
     }
 
+    // Hide the response viewer (eye) button when setting is disabled.
+    // Marker class, not inline style — the base rule is display:inline-flex !important.
+    const showResponseViewer = settings.showResponseViewer ?? defaults.showResponseViewer ?? true;
+    const responseViewerBtn = document.querySelector('.btn-response-viewer-header');
+    if (responseViewerBtn) {
+      responseViewerBtn.classList.toggle('btn-response-viewer-header--hidden', !showResponseViewer);
+    }
+
     // Multi-monitor button — hidden by default (App Settings → Display → "Header
     // Displays"). The server renders the correct initial state on every reload;
     // this handles a live toggle from a settings save (no reload). Toggle the
@@ -1937,6 +1947,7 @@ Object.assign(CodemanApp.prototype, {
         // are NOT display keys — they control server-side behavior and must sync from server.
         const displayKeys = new Set([
           'showFontControls', 'showSystemStats', 'showTokenCount', 'showCost',
+          'showLifecycleLog', 'showResponseViewer',
           'showMonitor', 'showProjectInsights', 'showFileBrowser', 'showSubagents',
           'subagentActiveTabOnly', 'tabTwoRows', 'localEchoEnabled', 'cjkInputEnabled', 'extendedKeyboardBar',
         ]);

src/web/public/styles.css

@@ -8115,6 +8115,12 @@ kbd {
   display: inline-flex !important;
 }
 
+/* "Response Viewer" header toggle (App Settings → Display) — must out-specify
+   the inline-flex !important above */
+.btn-response-viewer-header.btn-response-viewer-header--hidden {
+  display: none !important;
+}
+
 .response-viewer {
   display: none;
   position: fixed;

src/web/schemas.ts

@@ -290,6 +290,7 @@ export const SettingsUpdateSchema = z
     showTokenCount: z.boolean().optional(),
     showCost: z.boolean().optional(),
     showLifecycleLog: z.boolean().optional(),
+    showResponseViewer: z.boolean().optional(),
     showMonitor: z.boolean().optional(),
     showProjectInsights: z.boolean().optional(),
     showFileBrowser: z.boolean().optional(),