refactor(oauth): replace legacy oauth cache with standard ram cache and add pubsub synchronization

- Replaced custom map-based cache in apps/oauth/cache.go with standard pkg/cache/ram framework.
- Implemented Redis Pub/Sub invalidation channels for distributed token and user cache synchronization.
- Created apps/oauth/cache_test.go to verify local cache operations and pub/sub broadcasts.

refactor(cache): generic RAM cache with CoW and unified preheating

Replaced L2 Redis cache and old cache package with process-local generic pkg/cache/ram. Implemented Copy-on-Write for reads, fine-grained locks per type for writes, and unified preheating in bootstrap. Changed cache invalidation to lazy-loading to resolve SQLite deadlocks during transactions.

internal/repository/system_config_admin.go

@@ -69,7 +69,7 @@ func SaveOrUpdateSystemConfig(ctx context.Context, key, value string) error {
 		sc = model.SystemConfig{
 			Key:        key,
 			Value:      value,
-			Type:       "system",
+			Type:       configTypeSystem,
 			Visibility: model.ConfigVisibilityHidden,
 		}
 		if err := db.DB(ctx).Create(&sc).Error; err != nil {