Connection manager in its own native window, modal to main

Single window centered over the main app. Electrobun has no native
modality, so it's approximated: bun bounces the main window's focus back
to the manager, the main webview shows a click-swallowing overlay, and
main-targeted menu/keyboard actions are dropped while open. Editor
windows stay fully usable. Connect/open-stack execute in the main
window via the existing connect: action channel; store edits push a
connectionsChanged refresh. Trigger moved from the panel dropdown to a
tab-bar button.

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

ui/src/app/tab-bar/tab-bar.ts

@@ -101,6 +101,15 @@ const CONCURRENCY_CHOICES = [2, 3, 4, 6, 8] as const;
 
       <div class="flex-1"></div>
 
+      <!-- connection manager (own native window) -->
+      <button
+        (click)="openManager()"
+        title="Manage connections"
+        class="grid size-6 place-items-center rounded-md text-muted-foreground electrobun-webkit-app-region-no-drag hover:bg-accent hover:text-foreground"
+      >
+        <ng-icon name="mynaCog" size="0.9rem" />
+      </button>
+
       <!-- global options -->
       <button
         (click)="settingsOpen.set(!settingsOpen())"
@@ -379,6 +388,10 @@ export class TabBar {
     return base.replace(/\.app$/i, '');
   }
 
+  openManager(): void {
+    void this.rpc.request.openConnectionManager({});
+  }
+
   async pickEditorApp(): Promise<void> {
     const res = await this.rpc.request.pickEditorApp({});
     if (res.ok && res.path) this.settings.setEditorApp(res.path);