🔧 feat: add OpenTelemetry instrumentation to persistence layer

- Added persistence telemetry configuration option (telemetry.persistence.enabled)
- Created PersistenceTelemetryConfig struct for fine-grained control
- Added GetPersistenceTelemetryEnabled() helper method
- Implemented telemetry span creation in SQLite repository
- Added OpenTelemetry instrumentation to key repository methods:
  - CreateUser: Tracks user creation with error recording
  - GetUserByUsername: Tracks queries with username attribute
- Maintained backward compatibility - telemetry is optional and disabled by default
- Updated all tests to pass config parameter to repository constructor
- Added proper error recording and span attributes for observability

Benefits:
- Performance monitoring of database operations
- Flamegraph generation capability for persistence layer
- Distributed tracing across service boundaries
- Configurable instrumentation for production vs development

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

pkg/user/sqlite_repository.go

@@ -9,6 +9,10 @@ import (
 	"path/filepath"
 	"time"
 
+	"dance-lessons-coach/pkg/config"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/trace"
 	"gorm.io/driver/sqlite"
 	"gorm.io/gorm"
 	"gorm.io/gorm/logger"
@@ -16,14 +20,18 @@ import (
 
 // SQLiteRepository implements UserRepository using SQLite
 type SQLiteRepository struct {
-	db     *gorm.DB
-	dbPath string
+	db         *gorm.DB
+	dbPath     string
+	config     *config.Config
+	spanPrefix string
 }
 
 // NewSQLiteRepository creates a new SQLite repository
-func NewSQLiteRepository(dbPath string) (*SQLiteRepository, error) {
+func NewSQLiteRepository(dbPath string, config *config.Config) (*SQLiteRepository, error) {
 	repo := &SQLiteRepository{
-		dbPath: dbPath,
+		dbPath:     dbPath,
+		config:     config,
+		spanPrefix: "user.repo.",
 	}
 
 	if err := repo.initializeDatabase(); err != nil {
@@ -70,8 +78,17 @@ func (r *SQLiteRepository) initializeDatabase() error {
 
 // CreateUser creates a new user in the database
 func (r *SQLiteRepository) CreateUser(ctx context.Context, user *User) error {
+	// Create telemetry span
+	ctx, span := r.createSpan(ctx, "create_user")
+	if span != nil {
+		defer span.End()
+	}
+
 	result := r.db.WithContext(ctx).Create(user)
 	if result.Error != nil {
+		if span != nil {
+			span.RecordError(result.Error)
+		}
 		return fmt.Errorf("failed to create user: %w", result.Error)
 	}
 	return nil
@@ -79,12 +96,22 @@ func (r *SQLiteRepository) CreateUser(ctx context.Context, user *User) error {
 
 // GetUserByUsername retrieves a user by username
 func (r *SQLiteRepository) GetUserByUsername(ctx context.Context, username string) (*User, error) {
+	// Create telemetry span
+	ctx, span := r.createSpan(ctx, "get_user_by_username")
+	if span != nil {
+		defer span.End()
+		span.SetAttributes(attribute.String("username", username))
+	}
+
 	var user User
 	result := r.db.WithContext(ctx).Where("username = ?", username).First(&user)
 	if result.Error != nil {
 		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
 			return nil, nil
 		}
+		if span != nil {
+			span.RecordError(result.Error)
+		}
 		return nil, fmt.Errorf("failed to get user by username: %w", result.Error)
 	}
 	return &user, nil
@@ -172,3 +199,15 @@ func (r *SQLiteRepository) Close() error {
 	}
 	return sqlDB.Close()
 }
+
+// createSpan creates a new telemetry span if persistence telemetry is enabled
+func (r *SQLiteRepository) createSpan(ctx context.Context, operation string) (context.Context, trace.Span) {
+	if r.config == nil || !r.config.GetPersistenceTelemetryEnabled() {
+		return ctx, trace.SpanFromContext(ctx)
+	}
+
+	// Create a new span with the operation name
+	spanName := r.spanPrefix + operation
+	tr := otel.Tracer("user-repository")
+	return tr.Start(ctx, spanName)
+}