fix(gui): declare pkexec dependency for deb package (#2635)

The GUI shells out to pkexec for privilege elevation on Linux
(elevate/linux.rs). Since Debian 12 / Ubuntu 24.04, pkexec is shipped
as a standalone binary package split from policykit-1, so it is not
guaranteed to be installed. On such systems (e.g. a minimal Debian 13
desktop) installing the official deb succeeds but launching the GUI
panics with:

  Failed to run elevated command: No such file or directory (os error 2)

Add 'pkexec | policykit-1' to the deb bundle dependencies. The
alternation keeps the package installable on older releases where
pkexec still lives inside policykit-1 (e.g. Ubuntu 22.04), while
tauri-bundler continues to append the auto-detected webkit2gtk/gtk
dependencies.

easytier-gui/src-tauri/tauri.conf.json

@@ -14,7 +14,14 @@
       "icons/icon.icns",
       "icons/icon.ico"
     ],
-    "createUpdaterArtifacts": false
+    "createUpdaterArtifacts": false,
+    "linux": {
+      "deb": {
+        "depends": [
+          "pkexec | policykit-1"
+        ]
+      }
+    }
   },
   "productName": "easytier-gui",
   "version": "2.7.0",