Editor opens in native windows (one per file)

Real BrowserWindow per edited file with its own RPC instance, deduped by
sessionId+path. The same Angular bundle boots an editor-only root via
preload globals. Native close isn't cancellable in electrobun, so the
editor mirrors its draft to bun; traffic-light closes get a native
Save/Discard prompt after the fact, and failed saves park the draft in
the edit-leftovers dir. In-window closes (Cmd+W, Close) use a styled
prompt; the quit guard now also counts unsaved editors.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/main.ts

@@ -1,5 +1,9 @@
 import { bootstrapApplication } from '@angular/platform-browser';
 import { appConfig } from './app/app.config';
 import { App } from './app/app';
+import { EditorWindow } from './app/editor-window/editor-window';
+import { APP_MODE } from './app/platform';
 
-bootstrapApplication(App, appConfig).catch((err) => console.error(err));
+// One bundle, two window kinds: the preload global picks the root component.
+const root = APP_MODE === 'editor' ? EditorWindow : App;
+bootstrapApplication(root, appConfig).catch((err) => console.error(err));