feat(client+scripts): release 本地真测 — local_test.sh + 内核查找加 /opt/homebrew

- scripts/local_test.sh:一键构建 release macOS 包 + 配 sing-box 免密 sudoers
  (TUN 需 root)+ 前台运行真身(日志直出),让本地测试 = release 线上行为
- kernel_process 二进制查找兜底加 /opt/homebrew/bin/sing-box(Apple Silicon
  brew),release 包从 Finder/直接启动也能找到内核,免设 PANGOLIN_SINGBOX_BIN

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/bridge/kernel_process.dart

@@ -11,7 +11,8 @@
 //       2. <executable dir>/sing-box  (或 .exe)
 //       3. <executable dir>/../../Resources/sing-box  (macOS .app bundle)
 //       4. <project>/app/kernel/dist/desktop/<os>-<arch>/sing-box  (开发目录)
-//       5. /usr/local/bin/sing-box
+//       5. /opt/homebrew/bin/sing-box  (Apple Silicon brew)
+//       6. /usr/local/bin/sing-box     (Intel brew / Linux)
 //   · 配置 Clash API 端口: 由 spawn 调用方（DesktopVpnBridge）写入配置，
 //     或从配置文件读 experimental.clash_api.external_controller
 //
@@ -601,9 +602,13 @@ class DesktopKernelProcess implements KernelProcess {
       }
     }
 
-    // 系统 PATH 兜底
-    const fallback = '/usr/local/bin/sing-box';
-    if (await File(fallback).exists()) return fallback;
+    // 系统常见安装路径兜底(Apple Silicon brew / Intel·Linux brew)
+    for (final fallback in const [
+      '/opt/homebrew/bin/sing-box',
+      '/usr/local/bin/sing-box',
+    ]) {
+      if (await File(fallback).exists()) return fallback;
+    }
 
     throw FileSystemException(
       'sing-box binary not found. '