feat(desktop-client): derive stable client_id from machine identity

Generate the desktop client_id deterministically from OS machine identifiers
(IOPlatformUUID / MachineGuid / /etc/machine-id) scoped per
tenant+workspace+user, with a persisted UUID fallback when the OS lookup
fails. The renderer now requests the id over a new IPC bridge instead of
keeping a localStorage UUID, so reinstalls and storage clears no longer
fork into duplicate clients. Server enforces the id as required and
rejects empty/malformed UUIDs. Also harden bootstrap reveal flow and
single-instance exit so a second launch focuses the existing window.

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

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

@@ -15,7 +15,16 @@ declare global {
     desktopBridge: {
       app: {
         ping(): Promise<string>;
-        deviceInfo(): Promise<{ device_name: string; os: string; cpu_arch: string }>;
+        deviceInfo(): Promise<{
+          device_name: string;
+          os: string;
+          cpu_arch: string;
+        }>;
+        clientId(scope: {
+          tenant_id: number;
+          workspace_id: number;
+          user_id: number;
+        }): Promise<string>;
         runtimeSnapshot(): Promise<DesktopRuntimeSnapshot>;
         bindPublishAccount(platformId: string): Promise<DesktopAccountInfo>;
         refreshRuntimeAccounts(): Promise<null>;