feat: support macOS arm64 remote Agent hosts

Extend GoodBuddy Agent packaging, installation, SSH attachment, Runtime lifecycle, and Desktop package management to macOS arm64. Linux x64, Linux arm64, and Darwin arm64 share the existing signed catalog. Preserve Ask read-only behavior and Execute account permissions, and stop detached tool descendants during Mac cancellation.

Upgrade Desktop before publishing the first mixed-platform catalog because older Linux-only readers reject Darwin entries. Intel Macs are not supported; no launchd service or administrator access is required. This commit does not publish a release.

Validation: 3520 tests passed, 57 skipped; typecheck, lint, and development build passed. Real Mac installation, Ask/Execute, cancellation and reconnect passed; final Linux installation, Ask and reconnect passed. Nine real model requests were recorded.

Release note: 支持将 Apple Silicon Mac 用作远程项目 Host，可安装 macOS arm64 Agent 并使用 Ask、Execute 和断线重连；与 Linux 共用一个包目录，发布混合目录前需升级 Desktop。

FEATURES.md

@@ -123,12 +123,16 @@ otherwise.
   in the desktop package; switching projects updates only local selection and
   does not connect or download. Settings reads a small signed catalog and
   reports the local version, latest compatible online version, and update
-  state for Linux x64/arm64. Downloads occur only after a user action, and
+  state for Linux x64, Linux arm64, and macOS arm64. Intel Macs are not supported.
+  Downloads occur only after a user action, and
   packages can also be imported or exported offline. Each compound `.gbagent`
   package contains the Agent, fixed Node, and the compatible OpenCode Runtime
   maintained by the desktop source. Online sources follow the GitHub/Beijing
   OSS choice in About and Updates. The cumulative signed catalog binds minimum
-  Desktop version, Agent protocol, architecture, size, SHA-256, and fixed URL.
+  Desktop version, Agent protocol, platform, architecture, size, SHA-256, and fixed URL.
+  All three targets share one catalog. Users must upgrade Desktop before the
+  first mixed-platform catalog is published because older Linux-only readers
+  reject catalogs containing Darwin entries.
   The public-key registry accepts equivalent JSON whitespace and line endings
   while still strictly validating schema, Ed25519 keys, environment, and
   revocation; catalog, package, manifest, payload signatures, and streaming
@@ -150,7 +154,9 @@ otherwise.
   Prompt, provider, or tool replay observed. The current Agent source lock is
   `0.11.18`, while the current Desktop release candidate is `0.12.4`; formal
   publication status follows the separate Agent and Desktop
-  release channels.
+  release channels. Current macOS source has passed native package installation,
+  detached lifecycle, Attach, real Ask/Execute, and cancellation of tools in
+  separate process groups on a real Host; this does not imply publication.
 - [x] **Manual SSH Host environment provisioning source path**: After Host Key,
   authentication, and system probes succeed, GoodBuddy saves the Host and
   read-only probes the shared Agent/Runtime. Saving a Host or opening a project