fix: recover managed SSH Agent package release

Linux .gbagent extraction inherited permissive directory modes, so compound packages failed secure Runtime verification on POSIX runners. Package roots and nested bundle directories now use private modes.

The production workflow now uses one GoodBuddy Agent signing identity for the Agent, bundled Runtime, outer package, and catalog. The unpublished 0.11.2 candidate is carried forward as desktop and Agent 0.11.3 without a LoongArch preview.

Release note: 修复 Linux 上 Agent 包解压后无法通过权限验证的问题，并将复合包各层统一为一组 GoodBuddy Agent 发布密钥。

AGENTS.md

@@ -227,10 +227,10 @@ Release note: 修复左上角项目设置与消息通道项目设置不一致的
   the checked-in public key registry.
 - `.github/workflows/agent-release.yml` is the only production compound Agent
   publication path. It requires an annotated immutable Agent tag, the protected
-  `agent-signing` Environment, native x64/arm64 builds, production Agent and
-  Runtime signing-key preflights, a signed cumulative catalog, a non-Latest
-  GitHub Agent Release, and synchronized immutable Beijing OSS objects plus the
-  final signed latest-catalog pointer.
+  `agent-signing` Environment, native x64/arm64 builds, one production Agent
+  signing identity for every layer of the compound package and catalog, a
+  non-Latest GitHub Agent Release, and synchronized immutable Beijing OSS
+  objects plus the final signed latest-catalog pointer.
 - `.github/workflows/packages.yml` and `release:package` build only desktop
   products. Missing Agent packages, remote Runtime inputs, or Agent signing
   credentials must never block an ordinary desktop package or release.