fix: make PhoneRistrettoCache a singleton to prevent stale cache entries

Same bug pattern as UserRistrettoCache — PhoneRistrettoCache() created
a new ristretto cache on every call. PhoneRepository is used by
PhoneService, PhoneAPIKeyService, and NotificationService, each getting
a separate cache. Cache invalidations (Clear/Del) in one service had
no effect on the others, leading to stale phone data.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: AchoArnold

api/pkg/di/container.go

@@ -87,6 +87,7 @@ type Container struct {
 	logger               telemetry.Logger
 	attachmentRepository repositories.AttachmentRepository
 	userRistrettoCache   *ristretto.Cache[string, entities.AuthContext]
+	phoneRistrettoCache  *ristretto.Cache[string, *entities.Phone]
 }
 
 // NewLiteContainer creates a Container without any routes or listeners
@@ -1717,8 +1718,11 @@ func (container *Container) UserRepository() repositories.UserRepository {
 }
 
 // PhoneRistrettoCache creates an in-memory *ristretto.Cache[string, *entities.Phone]
-func (container *Container) PhoneRistrettoCache() (cache *ristretto.Cache[string, *entities.Phone]) {
-	container.logger.Debug(fmt.Sprintf("creating %T", cache))
+func (container *Container) PhoneRistrettoCache() *ristretto.Cache[string, *entities.Phone] {
+	if container.phoneRistrettoCache != nil {
+		return container.phoneRistrettoCache
+	}
+	container.logger.Debug(fmt.Sprintf("creating %T", container.phoneRistrettoCache))
 	ristrettoCache, err := ristretto.NewCache[string, *entities.Phone](&ristretto.Config[string, *entities.Phone]{
 		MaxCost:     5000,
 		NumCounters: 5000 * 10,
@@ -1727,6 +1731,7 @@ func (container *Container) PhoneRistrettoCache() (cache *ristretto.Cache[string
 	if err != nil {
 		container.logger.Fatal(stacktrace.Propagate(err, "cannot create user ristretto cache"))
 	}
+	container.phoneRistrettoCache = ristrettoCache
 	return ristrettoCache
 }