Enable updater artifacts and update signing key

- Add createUpdaterArtifacts: true to bundle config, which tells
  cargo tauri build to produce .sig files alongside installers
- Update pubkey to match regenerated key (now with password)
- Without createUpdaterArtifacts, no .sig or .tar.gz updater bundles
  are produced, so latest.json was never generated

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src-tauri/tauri.conf.json

@@ -35,6 +35,7 @@
   "bundle": {
     "active": true,
     "targets": "all",
+    "createUpdaterArtifacts": true,
     "icon": [
       "icons/32x32.png",
       "icons/128x128.png",
@@ -60,7 +61,7 @@
   },
   "plugins": {
     "updater": {
-      "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IDU4QUJENTA4RkQ4NzQyMEQKUldRTlFvZjlDTldyV0pqU1Vsd3Z0Vzk0cFZGK3VBVDBLRk1xcFJxbkJoVzdYd2VoRkRGK0QxSTgK",
+      "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IDFFNzUzMzhEOEY2MjNEMDMKUldRRFBXS1BqVE4xSG8vK0lkUWN4WnZQYVIrbmc4RmpoOGlJWTBLTE15RlIya3JvQisvdUR3a0QK",
       "endpoints": [
         "https://github.com/HazyResearch/OpenJarvis/releases/download/desktop-latest/latest.json"
       ]