feat(ui): fenêtres View système séparées — WebviewWindow Tauri + port WindowGateway (#23)

Détache les vues dans de vraies fenêtres système Tauri (multi-écran,
fullscreen). Backend : commandes de gestion de WebviewWindow, capabilities
et composition root. Frontend : nouveau port WindowGateway et son adaptateur
window, entrée panel-only ViewWindow/ViewPanelBody, détachement câblé dans
ProjectsView. QA vert : app-tauri 63, frontend typecheck + vitest 546/546.

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

frontend/src/app/main.tsx

@@ -4,6 +4,7 @@ import React from "react";
 import ReactDOM from "react-dom/client";
 
 import { App } from "./App";
+import { ViewWindow, parseViewWindowParams } from "./ViewWindow";
 import { DIProvider } from "./di";
 import "@/shared/styles/theme.css";
 
@@ -12,10 +13,18 @@ if (!root) {
   throw new Error("missing #root element");
 }
 
+// #23: a detached view window loads the SPA with `?panel=&project=`. When those
+// params are present and valid, render only that view; otherwise the full app.
+const viewParams = parseViewWindowParams(window.location.search);
+
 ReactDOM.createRoot(root).render(
   <React.StrictMode>
     <DIProvider>
-      <App />
+      {viewParams ? (
+        <ViewWindow panel={viewParams.panel} projectId={viewParams.projectId} />
+      ) : (
+        <App />
+      )}
     </DIProvider>
   </React.StrictMode>,
 );