fix(desktop): report real hostname/platform/arch in heartbeat

Renderer was registering clients with navigator.platform ("MacIntel") and
a hardcoded "renderer-preview" cpu_arch. Source device info from the main
process (os.hostname + process.platform/arch) via a new device-info IPC,
and let heartbeats always send the authoritative runtime values so stale
registrations self-heal.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop-client/src/renderer/env.d.ts

@@ -14,6 +14,7 @@ declare global {
     desktopBridge: {
       app: {
         ping(): Promise<string>;
+        deviceInfo(): Promise<{ device_name: string; os: string; cpu_arch: string }>;
         runtimeSnapshot(): Promise<DesktopRuntimeSnapshot>;
         bindPublishAccount(platformId: string): Promise<DesktopAccountInfo>;
         refreshRuntimeAccounts(): Promise<null>;