feat: DSH 悬浮窗 v0.1.0 — 原生置顶小窗 + 会话镜像 + 抓屏隐身

- shell: WinForms + WebView2 原生壳（无边框/置顶/固定位置/锁定尺寸/全屏/自适应缩放/截图排除）
- shell/ui.html: 自适应界面（工具栏、会话镜像区、底部聊天框、轮/步/tok/s/MTOK/缓存命中/上下文状态条、外观设置）
- lib/host.js: DSH 插件 Host 半（endpoint 写入、SSE 会话与指标快照、float_window Agent 工具）
- tools: WebView2 SDK 拉取、BOM 修复、Host 冒烟测试
- README: 架构、实测结论（WDA_EXCLUDEFROMCAPTURE、玻璃模式、DPI、WebView2 加载）

LICENSE

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+MIT License
+
+Copyright (c) 2026 jiangchen
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.