fix: resolve nil pubsub preventing live game updates

v.PubSub() was captured at startup before v.Start() initialized NATS,
so both stores held nil and notify() silently no-oped. Replace the
PubSub interface with a callback that evaluates v.PubSub() lazily at
call time.

game/store.go

@@ -6,10 +6,6 @@ import (
 	"sync"
 )
 
-type PubSub interface {
-	Publish(subject string, data []byte) error
-}
-
 type PlayerSession struct {
 	Player *Player
 }
@@ -25,8 +21,8 @@ type Persister interface {
 type GameStore struct {
 	games     map[string]*GameInstance
 	gamesMu   sync.RWMutex
-	persister Persister
-	pubsub    PubSub
+	persister  Persister
+	notifyFunc func(gameID string)
 }
 
 func NewGameStore() *GameStore {
@@ -39,14 +35,14 @@ func (gs *GameStore) SetPersister(p Persister) {
 	gs.persister = p
 }
 
-func (gs *GameStore) SetPubSub(ps PubSub) {
-	gs.pubsub = ps
+func (gs *GameStore) SetNotifyFunc(f func(gameID string)) {
+	gs.notifyFunc = f
 }
 
 func (gs *GameStore) makeNotify(gameID string) func() {
 	return func() {
-		if gs.pubsub != nil {
-			gs.pubsub.Publish("game."+gameID, nil)
+		if gs.notifyFunc != nil {
+			gs.notifyFunc(gameID)
 		}
 	}
 }