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。

docs/development/release-runbook.md

@@ -50,9 +50,9 @@ below.
   optional: users explicitly download a compatible compound `.gbagent` package
   from Settings or import one offline before GoodBuddy can install or update a
   Host.
-- Each independently published Linux x64 or arm64 `.gbagent` contains the
+- Each independently published Linux x64, Linux arm64, or macOS arm64 `.gbagent` contains the
   Agent daemon, pinned Node, and the desktop-maintained compatible OpenCode
-  Runtime. Build both architectures on native GitHub Actions runners from one
+  Runtime. Build all three targets on native GitHub Actions runners from one
   immutable `agent-v<agentVersion>` tag.
 - Keep the GoodBuddy Agent source, shared protocol/contracts, runtime lock,
   bundle tooling, and tests in this repository so a desktop commit identifies
@@ -66,7 +66,9 @@ below.
   digest, use only an ephemeral in-memory test signing identity, and verify the
   resulting compound package and deterministic archive. It must not read
   production signing secrets, publish installable release artifacts, or modify
-  the checked-in public key registry.
+  the checked-in public key registry. The Darwin arm64 target uses `macos-15`
+  and the same production locks. Native CI checks do not replace real Host
+  installation, Attach, Ask/Execute, and lifecycle validation during development.
 - `.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, one production
@@ -98,11 +100,18 @@ below.
   and are separate from desktop `v${package.version}` releases. Confirm the
   exact Agent release commit and tag with the user before creating or pushing
   either.
-- The tagged commit must be reachable from protected `main`. The two native
-  jobs build the compound x64/arm64 packages from the same source and locks;
+- The tagged commit must be reachable from protected `main`. The three native
+  jobs build Linux x64, Linux arm64, and Darwin arm64 packages from the same source and locks;
   the catalog job rejects missing architectures, changed bytes for an existing
-  version/architecture identity, invalid prior signatures, and incompatible
+  version/platform/architecture identity, invalid prior signatures, and incompatible
   matrix metadata.
+- All three targets share the existing signed `agent-catalog.json`. Before the
+  first mixed-platform catalog is published, release the Desktop reader that
+  accepts Darwin entries and document the required Desktop upgrade. Older
+  Desktop readers reject the entire mixed catalog and cannot check online Agent
+  updates; preserve their locally verified packages and immutable historical
+  releases. Do not introduce a second catalog or silently weaken package
+  signature and integrity verification.
 - Agent GitHub Releases are ordinary non-draft, non-prerelease releases but
   must use `--latest=false`; they must never replace the desktop release marked
   Latest. Publish immutable packages and the versioned catalog to