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）

tools/fix-bom.ps1

@@ -0,0 +1,20 @@
+# fix-bom.ps1 - ensure every .ps1 in this repo is UTF-8 WITH BOM.
+# Windows PowerShell 5.1 reads BOM-less .ps1 as ANSI/GBK, which corrupts non-ASCII
+# comments and can silently break parsing (observed: variables becoming empty).
+# ASCII-only on purpose: this file must survive being saved without a BOM.
+param([string]$Root)
+$ErrorActionPreference = 'Stop'
+if (-not $Root) { $Root = Split-Path -Parent (Split-Path -Parent $MyInvocation.MyCommand.Path) }
+$utf8Bom = New-Object System.Text.UTF8Encoding($true)
+$fixed = 0
+Get-ChildItem $Root -Recurse -File -Filter *.ps1 | Where-Object { $_.FullName -notmatch '\\\.cache\\' } | ForEach-Object {
+    $bytes = [System.IO.File]::ReadAllBytes($_.FullName)
+    $hasBom = $bytes.Length -ge 3 -and $bytes[0] -eq 0xEF -and $bytes[1] -eq 0xBB -and $bytes[2] -eq 0xBF
+    if (-not $hasBom) {
+        $text = [System.IO.File]::ReadAllText($_.FullName, [System.Text.Encoding]::UTF8)
+        [System.IO.File]::WriteAllText($_.FullName, $text, $utf8Bom)
+        Write-Host "[bom] + $($_.Name)"
+        $script:fixed++
+    }
+}
+Write-Host "[bom] done, fixed=$fixed"