feat(updater): apply updates silently on Windows (installMode quiet)

Set plugins.updater.windows.installMode to "quiet" so the auto-updater
applies updates with no installer window or progress dialog — the app
just downloads, swaps, and relaunches into the new version, rather than
flashing an installer that looks like a manual setup.

"quiet" needs no elevation for the per-user (currentUser) NSIS install we
ship, and install failures still reject through downloadAndInstall (the
launch flow logs them; the Settings checker surfaces them), so silent
mode doesn't hide errors. Switch to "passive" if a progress bar is ever
wanted.

Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

apps/desktop/src-tauri/tauri.conf.json

@@ -24,7 +24,10 @@
         "https://api.mcpmux.com/v1/update/latest.json",
         "https://github.com/mcpmux/mcp-mux/releases/latest/download/latest.json"
       ],
-      "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IDdCQUZGMEVCMEZBOTk5RTcKUldUbm1ha1A2L0N2ZTlOZjN5T3pGOHBHRUlibytMY2tPeWJkQ01heDJzdTJqK3B3a2lBdDZ1T1oK"
+      "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IDdCQUZGMEVCMEZBOTk5RTcKUldUbm1ha1A2L0N2ZTlOZjN5T3pGOHBHRUlibytMY2tPeWJkQ01heDJzdTJqK3B3a2lBdDZ1T1oK",
+      "windows": {
+        "installMode": "quiet"
+      }
     }
   },
   "app": {