Use show poe-main-status instead of per-port PoE command

show poe-port status rejects all argument formats on this firmware;
show poe-main-status gives overall PoE power and health data instead.

https://claude.ai/code/session_01JR2EMK7rwrZJowpstcaxQ6

switch_backend.py

@@ -476,7 +476,7 @@ def _poll_loop():
         try:
             data = {
                 "port_status":  read_cmd("show interfaces"),
-                "poe_status":   read_cmd("show poe-port status ALL"),
+                "poe_status":   read_cmd("show poe-main-status"),
                 "vlan_members": read_cmd("show vlan"),
                 "sys_info":     read_cmd("show sys-info"),
             }