feat: add sidebar brand customization

The primary sidebar brand was fixed to the built-in name, subtitle, and logo. Appearance settings now let users preview and save a custom brand name, localized Chinese and English subtitles, and a validated local PNG, JPEG, or WebP logo, with default-logo and full-reset actions.

Customization remains device-local and limited to the top-left brand area; installer, update, Agent, and protocol identities remain GoodBuddy. The desktop package version is now 0.11.6.

Release note: 新增“外观 → 品牌定制”，可修改左上角品牌名称、中英文副标题和本地 Logo，并支持实时预览、恢复默认及本机持久化。

src/shared/image-media-type.test.ts

@@ -0,0 +1,46 @@
+import { describe, expect, it } from 'vitest'
+import { detectSupportedImage } from './image-media-type'
+
+describe('supported image detection', () => {
+  it.each([
+    {
+      bytes: [0xff, 0xd8, 0xff],
+      extension: 'jpg',
+      mimeType: 'image/jpeg'
+    },
+    {
+      bytes: [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a],
+      extension: 'png',
+      mimeType: 'image/png'
+    },
+    {
+      bytes: [
+        0x52,
+        0x49,
+        0x46,
+        0x46,
+        0,
+        0,
+        0,
+        0,
+        0x57,
+        0x45,
+        0x42,
+        0x50
+      ],
+      extension: 'webp',
+      mimeType: 'image/webp'
+    }
+  ])('detects $mimeType bytes', ({ bytes, extension, mimeType }) => {
+    expect(detectSupportedImage(Uint8Array.from(bytes))).toEqual({
+      extension,
+      mimeType
+    })
+  })
+
+  it('rejects unsupported bytes', () => {
+    expect(() =>
+      detectSupportedImage(Uint8Array.from([1, 2, 3]))
+    ).toThrow('图片格式不受支持')
+  })
+})

src/shared/image-media-type.ts

@@ -0,0 +1,44 @@
+export type SupportedImageFormat = {
+  extension: 'jpg' | 'png' | 'webp'
+  mimeType: 'image/jpeg' | 'image/png' | 'image/webp'
+}
+
+function matchesAscii(
+  data: Uint8Array,
+  offset: number,
+  value: string
+): boolean {
+  return [...value].every(
+    (character, index) =>
+      data[offset + index] === character.charCodeAt(0)
+  )
+}
+
+export function detectSupportedImage(
+  data: Uint8Array
+): SupportedImageFormat {
+  if (
+    data.byteLength >= 3 &&
+    data[0] === 0xff &&
+    data[1] === 0xd8 &&
+    data[2] === 0xff
+  ) {
+    return { extension: 'jpg', mimeType: 'image/jpeg' }
+  }
+  if (
+    data.byteLength >= 8 &&
+    [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a].every(
+      (value, index) => data[index] === value
+    )
+  ) {
+    return { extension: 'png', mimeType: 'image/png' }
+  }
+  if (
+    data.byteLength >= 12 &&
+    matchesAscii(data, 0, 'RIFF') &&
+    matchesAscii(data, 8, 'WEBP')
+  ) {
+    return { extension: 'webp', mimeType: 'image/webp' }
+  }
+  throw new Error('图片格式不受支持')
+}