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/rpc.service.ts

@@ -17,6 +17,7 @@ export class RpcService {
   readonly sessionClosed = signal<SessionClosedEvent | null>(null);
 
   private rpc: ReturnType<typeof Electroview.defineRPC<AppRPC>> | undefined;
+  private ready: Promise<void> = Promise.resolve();
 
   constructor() {
     this.available = typeof window !== 'undefined' && '__electrobun' in window;
@@ -31,12 +32,36 @@ export class RpcService {
         },
       },
     });
-    new Electroview({ rpc: this.rpc });
+    const electroview = new Electroview({ rpc: this.rpc });
+
+    // Requests fired before the RPC WebSocket finishes connecting are lost, so
+    // everything below gates on it being open (services fire calls at startup).
+    const socket = electroview.bunSocket;
+    if (socket && socket.readyState !== WebSocket.OPEN) {
+      this.ready = new Promise((resolve) => {
+        socket.addEventListener('open', () => resolve(), { once: true });
+        socket.addEventListener('error', () => resolve(), { once: true });
+      });
+    }
+
   }
 
-  /** Typed request proxy: `await rpc.request.listDir({...})`. */
+  /** Typed request proxy: `await rpc.request.listDir({...})`. Waits for the bridge. */
   get request() {
-    if (!this.rpc) throw new Error('RPC is only available inside the desktop app');
-    return this.rpc.request;
+    const rpc = this.rpc;
+    if (!rpc) throw new Error('RPC is only available inside the desktop app');
+    const ready = this.ready;
+    return new Proxy({} as (typeof rpc)['request'], {
+      get:
+        (_target, method: string) =>
+        async (params?: unknown) => {
+          await ready;
+          const methods = rpc.request as unknown as Record<
+            string,
+            (p?: unknown) => Promise<unknown>
+          >;
+          return methods[method](params);
+        },
+    });
   }
 }