fix: restore packaged runtimes and ship macOS DMG only

Desktop 0.12.7 omitted OpenCode's offline node_modules because the resource
copier excludes node_modules at its source root. Copy from the parent and
verify every prepared configuration file in the final package. Bundle DSH
session projection with the unpacked Host instead of leaving an ASAR-only
external import, and reject external DeepSeek imports in shipped chunks.

Run packaged OpenCode plugin import and the real DSH UtilityProcess handshake
in Windows x64 CI before removing unpacked output. Add regressions using the
actual electron-builder copier and Vite externalization configuration.

Prepare approved Desktop 0.12.8 notes and change macOS defaults and CI to DMG
only. Update aggregation, website downloads and update readers for 12
installers and 20 assets. Current readers retain historical DMG/ZIP support;
the user accepts that older macOS GitHub readers and all older mirror readers
need manual upgrades. Agent remains 0.11.21, with no new Agent or LoongArch tag.

Validation: 3608 tests passed, 0 failed, 61 skipped across 339 files;
typecheck, lint, release-note validation, website static checks and 18 website
tests passed. No local production build or packaged-app launch was performed
at the user's request; actual packaged startup validation runs in CI.

Release note: 修复安装后 OpenCode 离线依赖缺失和 DeepSeek Harness Host 启动退出；macOS 改为仅提供 DMG，受影响旧版用户需从下载页手动升级。

docs/features/remote-host/technical-design.md

@@ -12,7 +12,7 @@ Linux x64/arm64、取消和离线 GoodBuddy 传输的真实 Host 验收。
 Windows 到 Linux x64 的安装、Agent-owned Prompt、Agent 本地模型 gateway、断线恢复、
 同一 OpenCode Session 续接、取消和终态清理已经使用真实模型与工具验证。Agent
 `0.11.14` 已通过独立 workflow 发布 Linux x64/arm64 复合包和签名累计目录；当前未发布
-Agent 源码 lock 为 `0.11.21`，Desktop 候选为 `0.12.7`，等待各自独立发布审批。
+Agent 源码 lock 为已发布的 `0.11.21`，Desktop 候选为 `0.12.8`；本次桌面打包修复不重发 Agent。
 现有源码显示本地与远端 OpenCode 原生 Task，并取消 GoodBuddy 对生产 Prompt 的
 固定墙钟总时限。失败的 `agent-v0.11.3` 保持不可变且未发布。