Warn when the info API's windows pipe is outside the protected namespace

A program reading the info API opens the pipe by name and has no owner
check of its own, so for a name any local user could create first,
whoever did would be answering its queries. nebula refuses to serve a
held name and logs it, but the program cannot tell. The daemon now warns
at bind when the configured name is not under
\\.\pipe\ProtectedPrefix\Administrators\, and the example config and
CHANGELOG say to put it there.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

examples/config.yml

@@ -272,7 +272,8 @@ punchy:
   #
   #info:
     #enabled: false
-    # The absolute path to listen on, or a full pipe name on Windows.
+    # The absolute path to listen on, or a full pipe name on Windows. Name a pipe under
+    # \\.\pipe\ProtectedPrefix\Administrators\.
     #socket: /var/run/nebula/info.sock
     # A group (or account/group/SID on Windows) that should be allowed to access the
     # socket. On Windows the group may read and write the pipe but not create an