Refactor Store into SessionStore; move domain SQL onto User/Question/Answer.

internal/store/postgres.go

@@ -48,34 +48,33 @@ func postgresDSN(raw string) (string, error) {
 }
 
 // OpenPostgres connects to Postgres, applies schema/migrations, and starts session cleanup.
-func OpenPostgres(databaseURL, schema string) (*Store, error) {
+func OpenPostgres(databaseURL, schema string) (*sql.DB, *SessionStore, error) {
 	dsn, err := postgresDSN(databaseURL)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	db, err := sql.Open("pgx", dsn)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	db.SetMaxOpenConns(20)
 	db.SetMaxIdleConns(5)
 	if err := db.Ping(); err != nil {
 		_ = db.Close()
-		return nil, fmt.Errorf("postgres ping: %w", err)
+		return nil, nil, fmt.Errorf("postgres ping: %w", err)
 	}
 	if err := applySchema(db, schema); err != nil {
 		_ = db.Close()
-		return nil, fmt.Errorf("apply schema: %w", err)
+		return nil, nil, fmt.Errorf("apply schema: %w", err)
 	}
 	if err := applySessionsSchema(db); err != nil {
 		_ = db.Close()
-		return nil, fmt.Errorf("apply sessions schema: %w", err)
+		return nil, nil, fmt.Errorf("apply sessions schema: %w", err)
 	}
 	if err := migrateUserProfileColumns(db); err != nil {
 		_ = db.Close()
-		return nil, fmt.Errorf("migrate profile columns: %w", err)
+		return nil, nil, fmt.Errorf("migrate profile columns: %w", err)
 	}
-	st := &Store{db: db}
-	st.initSessionStore(5 * time.Minute)
-	return st, nil
+	sessions := NewSessionStore(db, 5*time.Minute)
+	return db, sessions, nil
 }