Add tray desktop notification helper

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_tray_notify.py

@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+"""Desktop notification helper: notify-send when available, else no-op."""
+import subprocess
+import unittest
+
+from enodia_sentinel.tray import notify
+
+
+class TestNotify(unittest.TestCase):
+    def test_no_notify_send_is_noop(self):
+        calls = []
+
+        def runner(cmd):
+            calls.append(cmd)
+            return subprocess.CompletedProcess(cmd, 0)
+
+        used = notify.notify("t", "b", runner=runner, which=lambda _n: None)
+        self.assertFalse(used)
+        self.assertEqual(calls, [])
+
+    def test_uses_notify_send_with_app_name(self):
+        calls = []
+
+        def runner(cmd):
+            calls.append(cmd)
+            return subprocess.CompletedProcess(cmd, 0)
+
+        used = notify.notify("Title", "Body", runner=runner,
+                             which=lambda _n: "/usr/bin/notify-send")
+        self.assertTrue(used)
+        self.assertEqual(len(calls), 1)
+        self.assertIn("notify-send", calls[0][0])
+        self.assertIn("Title", calls[0])
+        self.assertIn("Body", calls[0])