P4: SFTP provider, connection store, connection manager UI

- SftpProvider (ssh2): password + key auth, keepalive, clean-dispose vs
  unexpected-close distinction, POSIX path helpers, s->ms attr normalization
- ConnectionStore: plain JSON at appDataDir, 0600, atomic writes, folders
- connect/disconnect + store CRUD handlers; sessionClosed push -> panels fall
  back to local and in-flight jobs fail
- UI: session dropdown per panel (local/saved connections/manage), disconnect
  button, connection manager modal (folders, edit form, save/connect)
- electrobun bundler: external cpu-features/*.node (ssh2 optional natives)
- RpcService: gate requests on RPC socket open; defer initial panel loads past
  first render
- verified against 192.168.10.122: full op matrix, upload/download/remote-remote
  recursive transfers, roundtrip integrity, recursive remote delete, store CRUD

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

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

@@ -9,7 +9,9 @@ import {
   viewChild,
 } from '@angular/core';
 import { NgIcon } from '@ng-icons/core';
-import type { FileEntry } from '@shared/types';
+import type { FileEntry, SavedConnection } from '@shared/types';
+import { ConnectionsService } from '../connections.service';
+import { DialogsService } from '../dialogs.service';
 import { FileActionsService } from '../file-actions.service';
 import { formatDate, formatSize } from '../format';
 import { PanelsService, type Side, type SortKey } from '../panels.service';
@@ -27,10 +29,14 @@ export class FilePanel {
   readonly panels = inject(PanelsService);
   readonly actions = inject(FileActionsService);
   readonly transfers = inject(TransfersService);
+  readonly connections = inject(ConnectionsService);
+  readonly dialogs = inject(DialogsService);
   readonly panel = computed(() => this.panels.get(this.side()));
   readonly isActive = computed(() => this.panels.activeSide() === this.side());
+  readonly isRemote = computed(() => this.panel().sessionId() !== 'local');
 
   readonly pathDraft = signal('');
+  readonly menuOpen = signal(false);
 
   private readonly listEl = viewChild.required<ElementRef<HTMLDivElement>>('list');
   private lastClickedIndex = 0;
@@ -52,6 +58,27 @@ export class FilePanel {
     this.panels.activeSide.set(this.side());
   }
 
+  pickLocal(): void {
+    this.menuOpen.set(false);
+    void this.panels.disconnectPanel(this.side());
+  }
+
+  pickConnection(connection: SavedConnection): void {
+    this.menuOpen.set(false);
+    this.activate();
+    void this.panels.connectPanel(this.side(), connection, connection.name);
+  }
+
+  openManager(): void {
+    this.menuOpen.set(false);
+    this.activate();
+    this.dialogs.manager.set(true);
+  }
+
+  disconnect(): void {
+    void this.panels.disconnectPanel(this.side());
+  }
+
   iconFor(entry: FileEntry): string {
     return entry.type === 'dir' ? 'mynaFolder' : 'mynaFile';
   }