fix: add _send_command delegating to _exec_ssh_command

netOrk's generic reboot helper (_do_reboot) calls conn._send_command()
which did not exist on ProxmoxDriver — the resulting AttributeError was
silently swallowed, so reboot commands never executed on Proxmox nodes.
Delegates to the existing _exec_ssh_command so all generic SSH-based
actions (reboot, dns_port check, etc.) work correctly.

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

napalm_proxmox/system_mixin.py

@@ -711,6 +711,18 @@ class ProxmoxSystemMixin:
             old_short, short_hostname, fqdn,
         )
 
+    # ------------------------------------------------------------------ #
+    # _send_command — generic SSH command helper used by netOrk core
+    # ------------------------------------------------------------------ #
+
+    def _send_command(self, command: str) -> str:
+        """Execute *command* on the node and return its output.
+
+        Delegates to _exec_ssh_command so that netOrk's generic helpers
+        (e.g. the reboot action) work without knowing the driver internals.
+        """
+        return self._exec_ssh_command(command)
+
     def get_disk_smart(self) -> dict:
         """Return SMART health data for all disks on this Proxmox node.