Devices: fixes from review round 12

- A reconnect while an install runs keeps the login it started with; a new
  one from ~/.ssh/config applies after.
- Frame > Open SSH goes through the server, so it uses the same headset and
  address as the app and refuses when there's none.
- A bare frame alias in use when a headset is set up stays selectable.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/test_link.py

@@ -278,6 +278,8 @@ class Connecting(unittest.TestCase):
         self.link.config_mtime = None
         self.link.watch_config()
         self.assertEqual(len(self.routes), routes)  # an install is running: not yet
+        self.link.connect(["dropped"])  # a reconnect meanwhile keeps the login it started with
+        self.assertIn("User=steamos", self.routes[-1][1])
         running[0] = 0
         self.link.watch_config()
         self.assertIn("User=deck", self.routes[-1][1])