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/testhelper/test_helper.go

@@ -36,6 +36,11 @@ func SetupTestEnvironment(t *testing.T) (*gorm.DB, *miniredis.Miniredis, func())
 		t.Fatalf("failed to open in-memory SQLite db: %v", err)
 	}
 
+	// Limit to 1 open connection for SQLite :memory: to keep the database in one shared connection
+	if sqlDB, err := sqliteDB.DB(); err == nil {
+		sqlDB.SetMaxOpenConns(1)
+	}
+
 	// AutoMigrate all tables
 	err = sqliteDB.AutoMigrate(
 		&model.User{},
@@ -77,6 +82,8 @@ func SetupTestEnvironment(t *testing.T) (*gorm.DB, *miniredis.Miniredis, func())
 	// Cleanup function
 	cleanup := func() {
 		runExtraCleanups()
+		repository.StopSystemConfigCacheListener()
+		repository.StopAuthSourceCacheListener()
 		repository.ResetSystemConfigRAMCacheForTest()
 		_ = redisClient.Close()
 		mr.Close()