Pulls the three remaining platform-shaped interfaces out of app/common/
and into platform/network/, platform/leaderboard/ and platform/game/,
each with a function accessor + true no-op stub backend matching the
existing platform/profile/ template. Drops the duplicate
PlatformNetworkManagerInterface.h that was a stale copy of the same
type. Existing app-side singletons (LeaderboardManager,
LinuxLeaderboardManager, IPlatformNetworkStub, LinuxGame) keep working
unchanged - the structural fix is just that the interface they depend
on now lives in platform/ where it belongs.
Drops the polymorphic XuiActionPayload variant and the per-pad
setXuiServerAction/getXuiServerAction polling on IGameServices in
favour of a std::variant of typed action structs in
minecraft/server/ServerAction.h. MinecraftServer owns the queue,
drains it from the tick loop via std::visit, and exposes
queueServerAction() that any thread can call. Eliminates the
dynamic_cast across the minecraft<-app boundary, the per-pad slot,
and two busy-wait-for-Idle loops.
