feat: add projects flow and consolidate default project handling

internal/localdb/migrations.go

@@ -1,6 +1,7 @@
 package localdb
 
 import (
+	"errors"
 	"fmt"
 	"log/slog"
 	"time"
@@ -36,6 +37,11 @@ var localMigrations = []localMigration{
 		name: "Ensure is_active defaults to true for existing configurations",
 		run:  backfillConfigurationIsActive,
 	},
+	{
+		id:   "2026_02_06_projects_backfill",
+		name: "Create default projects and attach existing configurations",
+		run:  backfillProjectsForConfigurations,
+	},
 }
 
 func runLocalMigrations(db *gorm.DB) error {
@@ -133,6 +139,59 @@ func backfillConfigurationIsActive(tx *gorm.DB) error {
 	return tx.Exec("UPDATE local_configurations SET is_active = 1 WHERE is_active IS NULL").Error
 }
 
+func backfillProjectsForConfigurations(tx *gorm.DB) error {
+	var owners []string
+	if err := tx.Model(&LocalConfiguration{}).
+		Distinct("original_username").
+		Pluck("original_username", &owners).Error; err != nil {
+		return fmt.Errorf("load owners for projects backfill: %w", err)
+	}
+
+	for _, owner := range owners {
+		project, err := ensureDefaultProjectTx(tx, owner)
+		if err != nil {
+			return err
+		}
+
+		if err := tx.Model(&LocalConfiguration{}).
+			Where("original_username = ? AND (project_uuid IS NULL OR project_uuid = '')", owner).
+			Update("project_uuid", project.UUID).Error; err != nil {
+			return fmt.Errorf("assign default project for owner %s: %w", owner, err)
+		}
+	}
+
+	return nil
+}
+
+func ensureDefaultProjectTx(tx *gorm.DB, ownerUsername string) (*LocalProject, error) {
+	var project LocalProject
+	err := tx.Where("owner_username = ? AND is_system = ? AND name = ?", ownerUsername, true, "Без проекта").
+		First(&project).Error
+	if err == nil {
+		return &project, nil
+	}
+	if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, fmt.Errorf("load system project for %s: %w", ownerUsername, err)
+	}
+
+	now := time.Now()
+	project = LocalProject{
+		UUID:          uuid.NewString(),
+		OwnerUsername: ownerUsername,
+		Name:          "Без проекта",
+		IsActive:      true,
+		IsSystem:      true,
+		CreatedAt:     now,
+		UpdatedAt:     now,
+		SyncStatus:    "pending",
+	}
+	if err := tx.Create(&project).Error; err != nil {
+		return nil, fmt.Errorf("create system project for %s: %w", ownerUsername, err)
+	}
+
+	return &project, nil
+}
+
 func chooseNonZeroTime(candidate time.Time, fallback time.Time) time.Time {
 	if candidate.IsZero() {
 		return fallback