feat(frontend): host les fenêtres plugin et l'API publique windows.open

Ajoute la vue window host qui charge le layout plugin dans une fenêtre OS
détachée, expose react/react-dom/jsx-runtime hébergés sous
frontend/public/plugin-host pour que le runtime SDK y résolve React, et
câble services.windows.open() côté runtime plugin (loader/services/registry).

npm test -- --run src/adapters/window.test.ts src/app/ViewWindow.test.tsx
  src/plugins/runtime/loader.test.ts src/plugins/runtime/services.test.ts : 39/39
npm run typecheck : OK
npm run build : OK

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

frontend/src/plugins/runtime/registry.ts

@@ -32,6 +32,7 @@ import type {
   ProjectGateway,
   SystemGateway,
   TerminalGateway,
+  WindowGateway,
   WorkStateGateway,
 } from "@/ports";
 
@@ -42,6 +43,7 @@ export interface PluginGatewaySet {
   terminal: TerminalGateway;
   agents: AgentGateway;
   system: SystemGateway;
+  window: WindowGateway;
   workState: WorkStateGateway;
   focusedProject: FocusedProjectGateway;
   pluginWorkspace: PluginWorkspaceGateway;