fix: sync title bar overlay colors with app theme

The Windows title bar overlay (minimize/maximize/close buttons) was
hardcoded to dark colors and did not update when switching themes.

- Add titleBarTheme helper that maps AppearanceTheme to overlay and
  background colors, using nativeTheme for the system preference
- Call applyTitleBarTheme from the setTheme IPC handler so the overlay
  updates immediately on theme change
- Apply persisted theme on startup so the overlay matches from launch

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/index.ts

@@ -3,6 +3,7 @@ import { app, BrowserWindow } from 'electron';
 import { registerIpcHandlers } from '@main/ipc/registerIpcHandlers';
 import { EryxAppService } from '@main/EryxAppService';
 import { createMainWindow } from '@main/windows/createMainWindow';
+import { applyTitleBarTheme } from '@main/windows/titleBarTheme';
 
 let mainWindow: BrowserWindow | undefined;
 let appService: EryxAppService | undefined;
@@ -13,6 +14,10 @@ async function bootstrap(): Promise<void> {
   mainWindow = createMainWindow();
   registerIpcHandlers(mainWindow, appService);
 
+  // Apply persisted theme to the title bar overlay
+  const workspace = await appService.loadWorkspace();
+  applyTitleBarTheme(mainWindow, workspace.settings.theme);
+
   if (!app.isPackaged) {
     mainWindow.webContents.openDevTools({ mode: 'detach' });
   }

src/main/ipc/registerIpcHandlers.ts

@@ -19,6 +19,7 @@ import type { QuerySessionsInput } from '@shared/domain/sessionLibrary';
 import type { AppearanceTheme } from '@shared/domain/tooling';
 
 import { EryxAppService } from '@main/EryxAppService';
+import { applyTitleBarTheme } from '@main/windows/titleBarTheme';
 
 export function registerIpcHandlers(window: BrowserWindow, service: EryxAppService): void {
   ipcMain.handle(ipcChannels.describeSidecarCapabilities, () => service.describeSidecarCapabilities());
@@ -34,9 +35,11 @@ export function registerIpcHandlers(window: BrowserWindow, service: EryxAppServi
   ipcMain.handle(ipcChannels.setPatternFavorite, (_event, input: SetPatternFavoriteInput) =>
     service.setPatternFavorite(input.patternId, input.isFavorite),
   );
-  ipcMain.handle(ipcChannels.setTheme, (_event, theme: AppearanceTheme) =>
-    service.setTheme(theme),
-  );
+  ipcMain.handle(ipcChannels.setTheme, async (_event, theme: AppearanceTheme) => {
+    const result = await service.setTheme(theme);
+    applyTitleBarTheme(window, theme);
+    return result;
+  });
   ipcMain.handle(ipcChannels.saveMcpServer, (_event, input: SaveMcpServerInput) =>
     service.saveMcpServer(input.server),
   );

src/main/windows/titleBarTheme.ts

@@ -0,0 +1,38 @@
+import { nativeTheme, type BrowserWindow } from 'electron';
+
+import type { AppearanceTheme } from '@shared/domain/tooling';
+
+interface TitleBarColors {
+  backgroundColor: string;
+  overlay: { color: string; symbolColor: string };
+}
+
+const darkColors: TitleBarColors = {
+  backgroundColor: '#09090b',
+  overlay: { color: '#09090b', symbolColor: '#a1a1aa' },
+};
+
+const lightColors: TitleBarColors = {
+  backgroundColor: '#ffffff',
+  overlay: { color: '#ffffff', symbolColor: '#52525b' },
+};
+
+function resolveEffectiveTheme(theme: AppearanceTheme): 'dark' | 'light' {
+  if (theme === 'light') return 'light';
+  if (theme === 'dark') return 'dark';
+  return nativeTheme.shouldUseDarkColors ? 'dark' : 'light';
+}
+
+function colorsForTheme(theme: AppearanceTheme): TitleBarColors {
+  return resolveEffectiveTheme(theme) === 'light' ? lightColors : darkColors;
+}
+
+export function applyTitleBarTheme(window: BrowserWindow, theme: AppearanceTheme): void {
+  const { backgroundColor, overlay } = colorsForTheme(theme);
+  window.setBackgroundColor(backgroundColor);
+
+  // setTitleBarOverlay is only available on Windows (and some Linux WMs).
+  if (typeof window.setTitleBarOverlay === 'function') {
+    window.setTitleBarOverlay(overlay);
+  }
+}