Redo connection manager: Stacks, More options, drag & drop, WinSCP import

Folders become Stacks (connections.json v2, no v1 migration): collapsible
stack-first list, open-stack-in-tabs (first reuses a pristine tab), drag
connections between stacks. More... reveals a per-connection Local
directory applied to the other panel when local and untouched. Import
reads a WinSCP.ini export incl. deobfuscated passwords.

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

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

@@ -89,7 +89,7 @@ export class FilePanel {
   pickConnection(connection: SavedConnection): void {
     this.menuOpen.set(false);
     this.activate();
-    void this.panels.connectPanel(this.side(), connection, connection.name);
+    void this.panels.connectPanel(this.side(), connection, connection.name, connection.localDir);
   }
 
   toggleMenu(): void {