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。

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "goodbuddy",
-  "version": "0.11.5",
+  "version": "0.11.6",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "goodbuddy",
-      "version": "0.11.5",
+      "version": "0.11.6",
       "license": "0BSD",
       "dependencies": {
         "@agentclientprotocol/sdk": "0.25.1",