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/app.ts

@@ -1,6 +1,7 @@
 import { Component, inject } from '@angular/core';
 import { NgIcon } from '@ng-icons/core';
 import { BRANDING } from '@shared/branding';
+import { ConnectionManager } from './connection-manager/connection-manager';
 import { ChmodDialog } from './dialogs/chmod-dialog';
 import { ConfirmDialog } from './dialogs/confirm-dialog';
 import { PromptDialog } from './dialogs/prompt-dialog';
@@ -14,7 +15,15 @@ import { TransfersService } from './transfers.service';
 
 @Component({
   selector: 'app-root',
-  imports: [NgIcon, FilePanel, PromptDialog, ConfirmDialog, ChmodDialog, TransferBar],
+  imports: [
+    NgIcon,
+    FilePanel,
+    PromptDialog,
+    ConfirmDialog,
+    ChmodDialog,
+    TransferBar,
+    ConnectionManager,
+  ],
   templateUrl: './app.html',
 })
 export class App {