RequestJoinGroup is a silent no-op when called on the server

`SCR_PlayerControllerGroupComponent.RequestJoinGroup()` is nothing but `Rpc(RPC_AskJoinGroup, groupID)`. An `RplRcver.Server` RPC. That only travels when the caller is a **proxy**. Vanilla calls this method from server-side code in at least two places, where the RPC is marshalled by the authority and goes nowhere, so the join simply never happens. ## Steps to reproduce (dedicated server) 1. Run a dedicated server. Player A creates a **private** group and is its leader. 2. Player B requests to join it (Request Join in the group menu). 3. Player A approves the request. ## Observed Nothing happens: player B stays in their old group. Worse, player B is sent the `GROUPS_REQUEST_ACCEPTED` notification (`:564`), so both players believe the join succeeded. The engine does not loop an RPC back to the machine that sends it, so on the authority this call is discarded and `RPC_AskJoinGroup` (`:873`) never runs. `:564` then sends `ENotification.GROUPS_REQUEST_ACCEPTED` regardless.

`SCR_PlayerControllerGroupComponent.RequestJoinGroup()` is nothing but `Rpc(RPC_AskJoinGroup, groupID)`. An `RplRcver.Server` RPC. That only travels when the caller is a **proxy**. Vanilla calls this method from server-side code in at least two places, where the RPC is marshalled by the authority and goes nowhere, so the join simply never happens.

## Steps to reproduce (dedicated server)

1. Run a dedicated server. Player A creates a **private** group and is its leader.
2. Player B requests to join it (Request Join in the group menu).
3. Player A approves the request.

## Observed

Nothing happens: player B stays in their old group. Worse, player B is sent the `GROUPS_REQUEST_ACCEPTED` notification (`:564`), so both players believe the join succeeded.

The engine does not loop an RPC back to the machine that sends it, so on the authority this call is discarded and `RPC_AskJoinGroup` (`:873`) never runs. `:564` then sends `ENotification.GROUPS_REQUEST_ACCEPTED` regardless.