feat(ui): add cross-platform window control styles

Persist automatic and explicit macOS, Windows, GNOME, and minimal control presets with localized settings and platform-aware fallback.

Refs #31

src/utils/windowControlStyle.test.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it } from 'vitest';
+import { resolveWindowControlStyle } from './windowControlStyle';
+
+describe('resolveWindowControlStyle', () => {
+  it('uses the platform convention for automatic style', () => {
+    expect(resolveWindowControlStyle('auto', 'macos')).toBe('macos');
+    expect(resolveWindowControlStyle('auto', 'windows')).toBe('windows');
+    expect(resolveWindowControlStyle('auto', 'linux')).toBe('gnome');
+  });
+
+  it('falls back to macOS styling while an unsupported platform is unresolved', () => {
+    expect(resolveWindowControlStyle('auto', 'unknown')).toBe('macos');
+    expect(resolveWindowControlStyle('auto', 'android')).toBe('macos');
+  });
+
+  it('uses the desktop user agent while native platform detection is unresolved', () => {
+    expect(resolveWindowControlStyle('auto', 'unknown', 'Mozilla/5.0 (Windows NT 10.0; Win64; x64)')).toBe('windows');
+    expect(resolveWindowControlStyle('auto', 'unknown', 'Mozilla/5.0 (X11; Linux x86_64)')).toBe('gnome');
+    expect(resolveWindowControlStyle('auto', 'unknown', 'Mozilla/5.0 (Linux; Android 14)')).toBe('macos');
+  });
+
+  it('preserves an explicit style across platforms', () => {
+    expect(resolveWindowControlStyle('macos', 'windows')).toBe('macos');
+    expect(resolveWindowControlStyle('windows', 'linux')).toBe('windows');
+    expect(resolveWindowControlStyle('gnome', 'macos')).toBe('gnome');
+    expect(resolveWindowControlStyle('minimal', 'windows')).toBe('minimal');
+  });
+});

src/utils/windowControlStyle.ts

@@ -0,0 +1,16 @@
+import type { WindowControlStyle } from '../bindings/WindowControlStyle';
+
+export type ResolvedWindowControlStyle = Exclude<WindowControlStyle, 'auto'>;
+
+export const resolveWindowControlStyle = (
+  style: WindowControlStyle,
+  os: string,
+  userAgent = ''
+): ResolvedWindowControlStyle => {
+  if (style !== 'auto') return style;
+  if (os === 'windows') return 'windows';
+  if (os === 'linux') return 'gnome';
+  if (os === 'unknown' && /Windows/i.test(userAgent)) return 'windows';
+  if (os === 'unknown' && /Linux/i.test(userAgent) && !/Android/i.test(userAgent)) return 'gnome';
+  return 'macos';
+};