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/app.ts

@@ -79,7 +79,12 @@ export class App {
       const id = action.slice('connect:'.length);
       const connection = this.connections.connections().find((c) => c.id === id);
       if (connection) {
-        void this.panels.connectPanel(this.panels.activeSide(), connection, connection.name);
+        void this.panels.connectPanel(
+          this.panels.activeSide(),
+          connection,
+          connection.name,
+          connection.localDir,
+        );
       }
       return;
     }