Complete foundational data layer with repository implementation

- Add GORM dependencies for SQLite and PostgreSQL
- Create domain models (User, Session, File) with common errors
- Implement repository interfaces and database layer with migrations
- Update WebApp to bootstrap with database and repositories
- Add comprehensive unit tests for repository methods
- Update config structure to support multiple database drivers
- Extend AGENTS.md with debugging principles and dependency rules

internal/app/webapp.go

@@ -1,19 +1,67 @@
 package app
 
 import (
+	"fmt"
+
+	"gorm.io/gorm"
+
 	"github.com/dhao2001/mygo/internal/config"
+	"github.com/dhao2001/mygo/internal/repository"
 )
 
 // WebApp contains application-wide runtime dependencies and metadata.
 type WebApp struct {
 	Config  *config.Config
 	Version string
+
+	DB          *gorm.DB
+	UserRepo    repository.UserRepository
+	SessionRepo repository.SessionRepository
+	FileRepo    repository.FileRepository
 }
 
-// NewWebApp creates the application dependency container for the HTTP server.
-func NewWebApp(cfg *config.Config) *WebApp {
+// Bootstrap creates a fully initialized WebApp from config.
+// It opens the database, runs migrations, and wires all repositories.
+func Bootstrap(cfg *config.Config) (*WebApp, error) {
+	db, err := repository.Open(cfg.Database)
+	if err != nil {
+		return nil, fmt.Errorf("open database: %w", err)
+	}
+
+	if err := repository.AutoMigrate(db); err != nil {
+		return nil, fmt.Errorf("migrate database: %w", err)
+	}
+
 	return &WebApp{
-		Config:  cfg,
-		Version: AppVersion,
+		Config:      cfg,
+		Version:     AppVersion,
+		DB:          db,
+		UserRepo:    repository.NewUserRepository(db),
+		SessionRepo: repository.NewSessionRepository(db),
+		FileRepo:    repository.NewFileRepository(db),
+	}, nil
+}
+
+// NewWebApp creates a WebApp with pre-built dependencies (useful for testing).
+func NewWebApp(cfg *config.Config, db *gorm.DB, userRepo repository.UserRepository, sessionRepo repository.SessionRepository, fileRepo repository.FileRepository) *WebApp {
+	return &WebApp{
+		Config:      cfg,
+		Version:     AppVersion,
+		DB:          db,
+		UserRepo:    userRepo,
+		SessionRepo: sessionRepo,
+		FileRepo:    fileRepo,
 	}
 }
+
+// Close releases resources held by the application (e.g., database connections).
+func (w *WebApp) Close() error {
+	if w.DB == nil {
+		return nil
+	}
+	sqlDB, err := w.DB.DB()
+	if err != nil {
+		return err
+	}
+	return sqlDB.Close()
+}

internal/app/webapp_test.go

@@ -9,7 +9,7 @@ import (
 func TestNewWebApp(t *testing.T) {
 	cfg := &config.Config{}
 
-	webApp := NewWebApp(cfg)
+	webApp := NewWebApp(cfg, nil, nil, nil, nil)
 
 	if webApp.Config != cfg {
 		t.Fatal("Config was not assigned")
@@ -18,3 +18,10 @@ func TestNewWebApp(t *testing.T) {
 		t.Errorf("Version = %q, want %q", webApp.Version, AppVersion)
 	}
 }
+
+func TestCloseNilDB(t *testing.T) {
+	webApp := NewWebApp(&config.Config{}, nil, nil, nil, nil)
+	if err := webApp.Close(); err != nil {
+		t.Errorf("Close with nil DB should not error: %v", err)
+	}
+}