feat(ui): integrate Electron mode detection for conditional UI rendering

- Added `isElectronMode` function to determine if the app is running in Electron or a browser.
- Updated `SidebarHeader`, `TabBar`, and `TabbedLayout` components to conditionally render UI elements based on the Electron mode.
- Adjusted styles and settings gear icon visibility to enhance user experience in browser mode.

This commit improves the application's adaptability by ensuring that Electron-specific features are only available when appropriate.

src/renderer/api/index.ts

@@ -39,6 +39,12 @@ function getImpl(): ElectronAPI {
  * In browser: delegates to `HttpAPIClient` (created on first use).
  * In tests: delegates to whatever mock is installed on `window.electronAPI`.
  */
+/**
+ * Whether the app is running inside Electron (true) or in a browser via HTTP server (false).
+ * Use this to hide Electron-only UI (settings, traffic lights, etc.) in browser mode.
+ */
+export const isElectronMode = (): boolean => !!window.electronAPI;
+
 export const api: ElectronAPI = new Proxy({} as ElectronAPI, {
   get(_target, prop, receiver) {
     const impl = getImpl();

src/renderer/components/layout/SidebarHeader.tsx

@@ -13,6 +13,7 @@
 
 import { useEffect, useRef, useState } from 'react';
 
+import { isElectronMode } from '@renderer/api';
 import { HEADER_ROW1_HEIGHT, HEADER_ROW2_HEIGHT } from '@renderer/constants/layout';
 import { useStore } from '@renderer/store';
 import { truncateMiddle } from '@renderer/utils/stringUtils';
@@ -330,8 +331,10 @@ export const SidebarHeader = (): React.JSX.Element => {
         style={
           {
             height: `${HEADER_ROW1_HEIGHT}px`,
-            paddingLeft: 'var(--macos-traffic-light-padding-left, 72px)',
-            WebkitAppRegion: 'drag',
+            paddingLeft: isElectronMode()
+              ? 'var(--macos-traffic-light-padding-left, 72px)'
+              : '16px',
+            WebkitAppRegion: isElectronMode() ? 'drag' : undefined,
           } as React.CSSProperties
         }
       >

src/renderer/components/layout/TabBar.tsx

@@ -11,6 +11,7 @@ import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 
 import { useDroppable } from '@dnd-kit/core';
 import { horizontalListSortingStrategy, SortableContext } from '@dnd-kit/sortable';
+import { isElectronMode } from '@renderer/api';
 import { HEADER_ROW1_HEIGHT } from '@renderer/constants/layout';
 import { useStore } from '@renderer/store';
 import { Bell, PanelLeft, Plus, RefreshCw, Search, Settings } from 'lucide-react';
@@ -250,7 +251,8 @@ export const TabBar = ({ paneId }: TabBarProps): React.JSX.Element => {
             sidebarCollapsed && isLeftmostPane
               ? 'var(--macos-traffic-light-padding-left, 72px)'
               : '8px',
-          WebkitAppRegion: sidebarCollapsed && isLeftmostPane ? 'drag' : undefined,
+          WebkitAppRegion:
+            isElectronMode() && sidebarCollapsed && isLeftmostPane ? 'drag' : undefined,
           backgroundColor: 'var(--color-surface)',
           borderBottom: '1px solid var(--color-border)',
           opacity: isFocused || paneCount === 1 ? 1 : 0.7,
@@ -382,20 +384,22 @@ export const TabBar = ({ paneId }: TabBarProps): React.JSX.Element => {
           )}
         </button>
 
-        {/* Settings gear icon */}
-        <button
-          onClick={openSettingsTab}
-          onMouseEnter={() => setSettingsHover(true)}
-          onMouseLeave={() => setSettingsHover(false)}
-          className="rounded-md p-2 transition-colors"
-          style={{
-            color: settingsHover ? 'var(--color-text)' : 'var(--color-text-muted)',
-            backgroundColor: settingsHover ? 'var(--color-surface-raised)' : 'transparent',
-          }}
-          title="Settings"
-        >
-          <Settings className="size-4" />
-        </button>
+        {/* Settings gear icon (Electron only - browser can't access native settings) */}
+        {isElectronMode() && (
+          <button
+            onClick={openSettingsTab}
+            onMouseEnter={() => setSettingsHover(true)}
+            onMouseLeave={() => setSettingsHover(false)}
+            className="rounded-md p-2 transition-colors"
+            style={{
+              color: settingsHover ? 'var(--color-text)' : 'var(--color-text-muted)',
+              backgroundColor: settingsHover ? 'var(--color-surface-raised)' : 'transparent',
+            }}
+            title="Settings"
+          >
+            <Settings className="size-4" />
+          </button>
+        )}
       </div>
 
       {/* Context menu */}

src/renderer/components/layout/TabbedLayout.tsx

@@ -6,6 +6,7 @@
  * - Main content: PaneContainer with one or more panes, each with TabBar + content
  */
 
+import { isElectronMode } from '@renderer/api';
 import { getTrafficLightPaddingForZoom } from '@renderer/constants/layout';
 import { useKeyboardShortcuts } from '@renderer/hooks/useKeyboardShortcuts';
 import { useZoomFactor } from '@renderer/hooks/useZoomFactor';
@@ -64,7 +65,7 @@ export const TabbedLayout = (): React.JSX.Element => {
   // Enable keyboard shortcuts
   useKeyboardShortcuts();
   const zoomFactor = useZoomFactor();
-  const trafficLightPadding = getTrafficLightPaddingForZoom(zoomFactor);
+  const trafficLightPadding = isElectronMode() ? getTrafficLightPaddingForZoom(zoomFactor) : 0;
 
   return (
     <div