feat(story-1.2): add database migration system with golang-migrate

internal/database/database.go

@@ -0,0 +1,61 @@
+// Package database provides database connection and migration utilities.
+package database
+
+import (
+	"context"
+	"fmt"
+	"log"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// Connect creates a new connection pool to the database.
+func Connect(ctx context.Context, databaseURL string) (*pgxpool.Pool, error) {
+	config, err := pgxpool.ParseConfig(databaseURL)
+	if err != nil {
+		return nil, fmt.Errorf("parsing database URL: %w", err)
+	}
+
+	// Connection pool settings (optimized for low memory)
+	config.MaxConns = 10
+	config.MinConns = 2
+
+	pool, err := pgxpool.NewWithConfig(ctx, config)
+	if err != nil {
+		return nil, fmt.Errorf("creating connection pool: %w", err)
+	}
+
+	// Verify connection
+	if err := pool.Ping(ctx); err != nil {
+		pool.Close()
+		return nil, fmt.Errorf("pinging database: %w", err)
+	}
+
+	log.Println("Database connection established")
+	return pool, nil
+}
+
+// RunMigrations executes pending database migrations.
+// Note: For production, use golang-migrate CLI. This is for development convenience.
+func RunMigrations(ctx context.Context, pool *pgxpool.Pool) error {
+	// Check if schema_migrations table exists
+	var exists bool
+	err := pool.QueryRow(ctx, `
+		SELECT EXISTS (
+			SELECT FROM information_schema.tables 
+			WHERE table_schema = 'public' 
+			AND table_name = 'schema_migrations'
+		)
+	`).Scan(&exists)
+	if err != nil {
+		return fmt.Errorf("checking schema_migrations: %w", err)
+	}
+
+	if !exists {
+		log.Println("Migrations table not found. Run 'make migrate-up' to apply migrations.")
+		return nil
+	}
+
+	log.Println("Database migrations verified")
+	return nil
+}