feat: preview Agent HTML in conversations and unblock long replies

Agent replies that produced HTML could only be read as source, so users had
to copy the markup into an external file to see the result. Completed Agent
and Subagent output now renders complete HTML documents, single-root HTML
replies, and `html` / `htm` code blocks as an isolated static preview in
place. Each preview keeps a persistent notice that scripts and network are
disabled and offers the same icon actions as Mermaid diagrams: a source
toggle and a full-screen preview. The new "render HTML in conversations"
switch under Platform Features / General is on by default, applies to the
open conversation immediately, and falls back to HTML source when disabled.
Previews cannot run scripts, reach the network, submit forms, open windows,
or load remote media; author stylesheets and inline styles are preserved so
the intended layout survives, and remote resource loading is refused by the
preview CSP instead.

Direct-model replies no longer fail once they grow large. The byte caps on
streaming responses, single stream blocks, non-streaming replies, model tool
arguments, tool request context, aggregate tool results, and accumulated
answer text are removed, so users stop seeing "模型接口流式响应超过安全限制"
on long answers. Response length is now governed by the request timeout,
cancellation, and context compression. Image generation responses keep their
decodable-image validation.

A message sent after a failed or interrupted run stayed in the pending queue
instead of running. The conversation is now released whenever a run reaches
any terminal state, not only when the renderer reports readiness again, and a
dispatched queue item whose run never starts releases its reservation and
returns to pending. Later messages dispatch without extra user action.

Release note: Agent 回复中的 HTML 现在可直接在会话内预览，支持查看源码和全屏预览，默认开启并可在“平台功能 / 通用设置”关闭；直连模型的长回复不再因大小限制中断；上一次运行失败或被中断后，新发送的消息会立即执行而不再排队等待。

FEATURES.zh-CN.md

@@ -18,7 +18,7 @@
 - [x] **可配置全局快捷唤起**：在“平台功能 / 通用设置”中启停或录制 Electron accelerator；默认保留 `CommandOrControl+Shift+Space`，冲突或保存失败时继续使用上一组已注册快捷键，并显示可处理的状态。
 - [x] **Projects、独立对话与会话分支**：按项目隔离上下文，管理会话、附件和 Git 工作区变更；本地会话可在稳定状态下复制当前聊天内容到独立分支，分支持续显示来源徽标且不复制 Task、队列或成果归属；项目选择器区分本地、托管 SSH 与远程消息通道项目，托管 SSH 项目按 Host 分组并在 Host 标题显示真实 Agent 连接状态，项目行只保留远端路径。
 - [x] **文件、截图、窗口、剪贴板上下文**：用户明确选择后才加入模型上下文。
-- [x] **富文本回答**：支持 GitHub Flavored Markdown、LaTeX 数学公式和受控 Mermaid 图表；大图可缩放、拖动或查看源码，失败时保留原始图表代码。
+- [x] **富文本回答**：支持 GitHub Flavored Markdown、LaTeX 数学公式、受控 Mermaid 图表和会话内 HTML 静态预览。Agent 完成回复后，完整 HTML 与 HTML 代码块可在原位置预览，并通过图标按钮查看源码或打开全屏预览；该能力默认开启，可在“平台功能 / 通用设置”关闭，预览不执行脚本、联网、表单提交或窗口操作。
 - [x] **AI 回复与完整会话复制**：已完成的 AI 回复可从消息底部复制不含推理、工具日志和引用元数据的 Markdown 原文；完整会话复制复用同一条经过 Preload/Main 校验的剪贴板路径。
 - [x] **助手工作栏、多终端与可调布局**：右侧工作栏使用持久“+”能力目录和应用 Tab；用户可为当前本机或托管 SSH 项目打开多个独立终端，获得有界输出、调整尺寸、结束与显式重连。关闭终端 Tab 会结束 Shell，应用重启只恢复已结束的 Tab 描述，不自动重启 Shell。主侧栏和魔法笔记列表支持鼠标与键盘调宽，魔法笔记列表可隐藏并记住布局，窄宽度下自动堆叠。
 - [ ] **项目 Agent Space**（规划中）：在 Project 中统一角色、知识、Skills/MCP、模型、审批策略、预算和超时，并支持模板复用。