feat: add Go password session lifecycle

backend/internal/postgres/database.go

@@ -56,20 +56,36 @@ type Querier interface {
 	Query(context.Context, string, ...any) (Rows, error)
 }
 
+type Transaction interface {
+	Querier
+	Exec(context.Context, string, ...any) error
+	Commit(context.Context) error
+	Rollback(context.Context) error
+}
+
+type TransactionBeginner interface {
+	Begin(context.Context) (Transaction, error)
+}
+
 type Pool interface {
 	Querier
 	Close()
 }
 
 type Database struct {
-	config  Config
-	querier Querier
+	config       Config
+	querier      Querier
+	transactions TransactionBeginner
 }
 
 type Store = Database
 
 func NewDatabase(config Config, querier Querier) *Database {
-	return &Database{config: config, querier: querier}
+	db := &Database{config: config, querier: querier}
+	if transactions, ok := querier.(TransactionBeginner); ok {
+		db.transactions = transactions
+	}
+	return db
 }
 
 func (db *Database) Readiness(ctx context.Context) error {