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/file-panel/file-panel.html

@@ -140,14 +140,6 @@
         }
       }
 
-      <div class="my-1 border-t border-border"></div>
-      <button
-        (click)="openManager()"
-        class="flex w-full items-center gap-2 px-3 py-1.5 text-left text-(length:--path-font) hover:bg-accent"
-      >
-        <ng-icon name="mynaCog" size="var(--action-icon)" class="shrink-0 text-muted-foreground" />
-        Manage connections…
-      </button>
     </div>
   }
 </div>

ui/src/app/file-panel/file-panel.ts

@@ -121,12 +121,6 @@ export class FilePanel {
     return `${host.username}@${host.hostname}:${host.port}`;
   }
 
-  openManager(): void {
-    this.menuOpen.set(false);
-    this.activate();
-    this.dialogs.manager.set(true);
-  }
-
   iconFor(entry: FileEntry): string {
     return fileGlyph(entry, this.settings.iconColors() === 'multi');
   }