P1: typed RPC bridge + FileSystemProvider + dual-panel local browsing

- shared/types + shared/rpc: full wire contract (Result envelope, no exceptions cross the bridge)
- FileSystemProvider interface, LocalProvider, SessionRegistry with built-in 'local'
- walk.ts: provider-generic recursive walk + removeRecursive
- rpc-handlers wired into BrowserWindow; 10min request timeout for slow SFTP ops
- Angular: RpcService (Electroview bridge + plain-browser guard), PanelsService with
  signals-based PanelState (sort/cursor/selection), FilePanel component with
  keyboard nav (arrows/Space/Enter/Backspace/Tab), path bar, toasts
- verified: both panels listDir home over the bridge in the running app

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

ui/src/app/rpc.service.ts

@@ -0,0 +1,42 @@
+import { Injectable, signal } from '@angular/core';
+import { Electroview } from 'electrobun/view';
+import type { AppRPC } from '@shared/rpc';
+import type { TransferSnapshot } from '@shared/types';
+
+// Matches MAX_REQUEST_TIME_MS on the bun side — SFTP ops can be slow.
+const MAX_REQUEST_TIME_MS = 10 * 60_000;
+
+export type SessionClosedEvent = { sessionId: string; reason: string };
+
+@Injectable({ providedIn: 'root' })
+export class RpcService {
+  /** False when the page is opened in a plain browser instead of the app. */
+  readonly available: boolean;
+
+  readonly transferUpdate = signal<TransferSnapshot | null>(null);
+  readonly sessionClosed = signal<SessionClosedEvent | null>(null);
+
+  private rpc: ReturnType<typeof Electroview.defineRPC<AppRPC>> | undefined;
+
+  constructor() {
+    this.available = typeof window !== 'undefined' && '__electrobun' in window;
+    if (!this.available) return;
+
+    this.rpc = Electroview.defineRPC<AppRPC>({
+      maxRequestTime: MAX_REQUEST_TIME_MS,
+      handlers: {
+        messages: {
+          transferUpdate: (snapshot) => this.transferUpdate.set(snapshot),
+          sessionClosed: (event) => this.sessionClosed.set(event),
+        },
+      },
+    });
+    new Electroview({ rpc: this.rpc });
+  }
+
+  /** Typed request proxy: `await rpc.request.listDir({...})`. */
+  get request() {
+    if (!this.rpc) throw new Error('RPC is only available inside the desktop app');
+    return this.rpc.request;
+  }
+}