Guard null Controller.Value in trigger hooks (fixes recurring 'Object reference not set', #178)

[RTN-VMR]

Summary

Four trigger-output hooks in TriggerHooks.cs dereference a pawn's controller with .Value! and no null check:

var player = new CCSPlayerController(new CCSPlayerPawn(activator.Handle).Controller.Value!.Handle);

(the trigger_multiple OnStartTouch/OnEndTouch and the two trigger_teleport equivalents). When a pawn has no controller, transient during disconnect or a round/map transition, .Value is null and .Value!.Handle throws NullReferenceException. Each hook has a surrounding try/catch that logs Object reference not set to an instance of an object. and continues, so it is not fatal, but on a busy server it fires constantly and the repeated throw/catch is measurable overhead. This is the symptom reported in #178.

Fix

Resolve .Controller.Value into a local, null-check it, and return HookResult.Continue when null, identical to the existing activator == null guards already in these methods. Behaviour is unchanged when the controller is present. Applied to all four sites.

Testing

Built clean (0/0). Verified live on a surf server: the recurring trigger_multiple OnEndTouch "Object reference not set" spam is gone.

Closes #178.