feat(desktop): add Electron desktop shell over the web profile

Spawn the real dsh CLI running the web profile on loopback (OS-assigned
port), parse the printed readiness URL, and open a native window at it.
The harness and its native addons stay on the system Node ABI; the main
imports only electron and node builtins.

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

apps/desktop/tests/ready-port.spec.ts

@@ -0,0 +1,17 @@
+import { describe, expect, it } from 'vitest'
+import { parseReadyPort } from '../src/ready-port.ts'
+
+describe('parseReadyPort', () => {
+  it('extracts the port from a complete readiness line', () => {
+    expect(parseReadyPort('dsh web: http://127.0.0.1:38291')).toBe(38291)
+  })
+
+  it('ignores lines without a readiness URL', () => {
+    expect(parseReadyPort('loading plugins…')).toBeUndefined()
+    expect(parseReadyPort('http://192.168.1.5:8080')).toBeUndefined()
+  })
+
+  it('matches the loopback URL before a LAN suffix on the same line', () => {
+    expect(parseReadyPort('dsh web: http://127.0.0.1:38291 (LAN: http://192.168.1.5:8080)')).toBe(38291)
+  })
+})