fix(wifi): remove PMF setting from open AP profile — breaks nmcli connection add on Trixie NM 1.52+

802-11-wireless-security.pmf is only valid within a security section that also
includes key-mgmt. Adding it to an open-network profile causes NM 1.52+ to
reject the connection add with 'key-mgmt: property is missing'. PMF has no
meaning for open APs (it only applies to WPA2/WPA3), so the setting is simply
removed rather than worked around.

Found by testing on devpi (Trixie, NM 1.52.1).

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

src/wifi_manager.py

@@ -2007,10 +2007,10 @@ class WiFiManager:
                 # No 802-11-wireless-security section → open network
             ]
 
-            # On Trixie disable PMF which can prevent older clients from connecting
+            # PMF (Protected Management Frames) is only meaningful for WPA2/WPA3.
-            if self._is_trixie:
+            # An open AP has no security section, so adding 802-11-wireless-security.pmf
-                cmd += ["802-11-wireless-security.pmf", "disable"]
+            # would cause NM to require key-mgmt too, breaking the connection add on
-                logger.info("Trixie detected: disabling PMF for better client compatibility")
+            # Trixie NM 1.52+. Leave PMF untouched — open APs have no frame protection.
 
             result = subprocess.run(cmd, capture_output=True, text=True, timeout=30)