Prefix plugin logs with LocalPlayerId

Add a per-instance local-player log prefix and apply it to networking and main plugin logs to make shared Fallout4Together.log entries readable when multiple instances run. Introduces F4T::Networking::GetLocalPlayerLogPrefix() (declared in F4TNetworking.h, implemented in F4TNetworking.cpp) and updates numerous REX::INFO/WARN calls to include the prefix. Also: only log sent player transforms after SendTransformPacket succeeds, add a small TODO comment about per-instance log files, and update docs (dev-log.md and plugin/setup.md) and the setup checklist to reflect the prefixed logging behavior. The prefix reads the assigned player ID via the thread-safe remote-player accessor and defaults to "[LocalPlayerId=unassigned]" before assignment.

plugin/include/F4TNetworking.h

@@ -1,9 +1,11 @@
 #pragma once
 
 #include <cstdint>
+#include <string>
 
 namespace F4T::Networking
 {
+	std::string GetLocalPlayerLogPrefix();
 	bool ConnectToLocalServer();
 	void DisconnectFromLocalServer();
 	bool IsConnectedToServer();