feat(desktop): 工业化升级 B —— 真桌面集成（Wails Go 桥 + 原生能力）

让它真正像桌面 App 而非套壳网页：启用闲置的 Wails Go 桥，接原生文件框/系统打开/
通知/无边框标题栏，且全部对浏览器预览（make web）优雅降级。

- app.go：SaveReportAs（原生"另存为"框 + 下载落盘）、OpenReport（下到临时目录 +
  系统默认应用打开 docx）、Notify（macOS osascript 通知）、download/openInSystem 跨平台
- main.go：macOS TitleBarHiddenInset —— 隐藏标题栏、内容铺满到顶、保留红绿灯交通灯
- lib/desktop.ts：window.go.main.App 运行时桥 + isDesktop/isMacDesktop 探测；
  saveReportAs/openReport/notify 在无 Wails（浏览器）时分别降级为 <a download>/新标签/Toast
- ReportView：桌面端「另存为 Word」(原生框) +「用系统打开」+ 完成弹系统通知；
  浏览器端保持「下载 Word」
- KbView：拖拽文件入库（HTML5 dataTransfer，两种模式通用）+ 拖拽高亮 +「选择文件」按钮
- TopBar：顶栏设为 Wails 可拖拽区（--wails-draggable），控件标 no-drag；
  macOS 桌面端左留白让位交通灯

验证：GOWORK=off wails build 打出 .app（绑定生成 + mac 标题栏）；启动真实原生窗口
截图确认无边框标题栏 + 交通灯内嵌 + 顶栏可拖拽（见会话截图）；浏览器(Preview)确认
window.go 不存在时降级正确（下载链路 + 拖拽占位）。tsc + vite build 通过。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sundynix-desktop/frontend/src/shell/TopBar.tsx

@@ -1,8 +1,14 @@
+import type { CSSProperties } from "react";
 import { User, ChevronDown } from "lucide-react";
 import type { Identity } from "../lib/api";
 import { useHealth } from "../lib/health";
+import { isMacDesktop } from "../lib/desktop";
 import { cn } from "../ui";
 
+// Wails 拖拽区/控件 CSS 变量（浏览器忽略，桌面端生效）。
+const DRAG = { "--wails-draggable": "drag" } as CSSProperties;
+const NODRAG = { "--wails-draggable": "no-drag" } as CSSProperties;
+
 function Light({ on, label, unknown }: { on?: boolean; label: string; unknown?: boolean }) {
   const dot = unknown ? "bg-slate-600" : on ? "bg-success shadow-[0_0_8px_rgba(52,211,153,0.7)]" : "bg-danger";
   return (
@@ -17,14 +23,17 @@ function Light({ on, label, unknown }: { on?: boolean; label: string; unknown?:
 export function TopBar({ identity, setIdentity }: { identity: Identity; setIdentity: (id: Identity) => void }) {
   const h = useHealth();
   return (
-    <header className="flex h-12 shrink-0 items-center gap-3 border-b border-line bg-ink-900/80 px-3 backdrop-blur">
+    <header
+      style={DRAG}
+      className={cn("flex h-12 shrink-0 items-center gap-3 border-b border-line bg-ink-900/80 pr-3 backdrop-blur", isMacDesktop() ? "pl-20" : "pl-3")}
+    >
       <div className="flex items-center gap-2">
         <div className="flex h-6 w-6 items-center justify-center rounded-md bg-gradient-to-br from-brand to-accent text-xs font-bold text-white">
           S
         </div>
         <span className="brand-gradient text-sm font-semibold">sundynix-agentix</span>
       </div>
-      <div className="relative">
+      <div className="relative" style={NODRAG}>
         <select
           className="appearance-none rounded-md border border-line bg-ink-800 py-1 pl-2.5 pr-7 text-xs text-slate-300 focus:border-brand focus:outline-none"
           defaultValue="通用版"
@@ -42,7 +51,7 @@ export function TopBar({ identity, setIdentity }: { identity: Identity; setIdent
         <Light unknown label="Milvus" />
         <Light unknown label="Neo4j" />
       </div>
-      <div className="ml-auto flex items-center gap-2">
+      <div className="ml-auto flex items-center gap-2" style={NODRAG}>
         <div className="relative">
           <User className="pointer-events-none absolute left-2 top-1/2 h-3.5 w-3.5 -translate-y-1/2 text-slate-500" />
           <input