feat: add brand asset upload with PNG conversion and improve config validation

- Add file upload support for logo and favicon with automatic PNG conversion
- Add backend validation for brand asset data URLs (app_logo, app_favicon)
- Change vite_config.value column type from varchar(200) to text for PostgreSQL
- Add schema migration v3 for vite_config.value column type conversion
- Update frontend to use file picker instead of manual URL input
- Add early favicon application in index.html to prevent flash

go-backend/internal/store/model/model.go

@@ -214,7 +214,7 @@ func (GroupPermissionGrant) TableName() string { return "group_permission_grant"
 type ViteConfig struct {
 	ID    int64  `gorm:"primaryKey;autoIncrement" json:"id"`
 	Name  string `gorm:"type:varchar(200);not null;uniqueIndex" json:"name"`
-	Value string `gorm:"type:varchar(200);not null" json:"value"`
+	Value string `gorm:"type:text;not null" json:"value"`
 	Time  int64  `gorm:"not null" json:"time"`
 }
 

go-backend/internal/store/repo/repository.go

@@ -2482,9 +2482,10 @@ func (r *Repository) GetUserTunnelByID(id int64) (*model.UserTunnel, error) {
 
 // ─── Migration ───────────────────────────────────────────────────────
 
-const currentSchemaVersion = 2
+const currentSchemaVersion = 3
 
 var ensurePostgresIDDefaultsFn = ensurePostgresIDDefaults
+var migrateViteConfigValueColumnTypeFn = migrateViteConfigValueColumnType
 
 func getSchemaVersion(db *gorm.DB) int {
 	var v model.SchemaVersion
@@ -2536,10 +2537,55 @@ func migrateSchema(db *gorm.DB) error {
 		return err
 	}
 
+	if ver < 3 {
+		if err := migrateViteConfigValueColumnTypeFn(db); err != nil {
+			return err
+		}
+	}
+
 	setSchemaVersion(db, currentSchemaVersion)
 	return nil
 }
 
+func migrateViteConfigValueColumnType(db *gorm.DB) error {
+	if db == nil {
+		return errors.New("nil db")
+	}
+
+	if !db.Migrator().HasTable(&model.ViteConfig{}) {
+		return nil
+	}
+
+	if db.Dialector.Name() != "postgres" {
+		return nil
+	}
+
+	type columnRow struct {
+		DataType string `gorm:"column:data_type"`
+	}
+
+	var row columnRow
+	if err := db.Raw(
+		`SELECT data_type FROM information_schema.columns
+		 WHERE table_schema = current_schema()
+		   AND table_name = ?
+		   AND column_name = ?`,
+		"vite_config", "value",
+	).Scan(&row).Error; err != nil {
+		return fmt.Errorf("inspect vite_config.value type: %w", err)
+	}
+
+	if strings.EqualFold(row.DataType, "text") {
+		return nil
+	}
+
+	if err := db.Exec(`ALTER TABLE "vite_config" ALTER COLUMN "value" TYPE TEXT`).Error; err != nil {
+		return fmt.Errorf("alter vite_config.value to text: %w", err)
+	}
+
+	return nil
+}
+
 func ensurePostgresIDDefaults(db *gorm.DB) error {
 	if db.Dialector.Name() != "postgres" {
 		return nil

go-backend/internal/store/repo/repository_migrate_test.go

@@ -83,3 +83,95 @@ func TestMigrateSchemaReturnsPostgresIDRepairError(t *testing.T) {
 		t.Fatalf("expected error %v, got %v", wantErr, err)
 	}
 }
+
+func TestMigrateSchemaRunsViteConfigValueMigrationForLegacySchema(t *testing.T) {
+	db, err := gorm.Open(gsqlite.Open(":memory:"), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	t.Cleanup(func() {
+		sqlDB, _ := db.DB()
+		if sqlDB != nil {
+			_ = sqlDB.Close()
+		}
+	})
+
+	if err := db.Exec(`CREATE TABLE schema_version (version INTEGER NOT NULL DEFAULT 0)`).Error; err != nil {
+		t.Fatalf("create schema_version: %v", err)
+	}
+	if err := db.Exec(`INSERT INTO schema_version(version) VALUES(?)`, 2).Error; err != nil {
+		t.Fatalf("seed schema_version: %v", err)
+	}
+
+	originalIDRepair := ensurePostgresIDDefaultsFn
+	ensurePostgresIDDefaultsFn = func(db *gorm.DB) error {
+		return nil
+	}
+	t.Cleanup(func() {
+		ensurePostgresIDDefaultsFn = originalIDRepair
+	})
+
+	called := 0
+	originalMigrate := migrateViteConfigValueColumnTypeFn
+	migrateViteConfigValueColumnTypeFn = func(db *gorm.DB) error {
+		called++
+		return nil
+	}
+	t.Cleanup(func() {
+		migrateViteConfigValueColumnTypeFn = originalMigrate
+	})
+
+	if err := migrateSchema(db); err != nil {
+		t.Fatalf("migrateSchema: %v", err)
+	}
+
+	if called != 1 {
+		t.Fatalf("expected vite_config migration to run once, got %d", called)
+	}
+}
+
+func TestMigrateSchemaReturnsViteConfigMigrationError(t *testing.T) {
+	db, err := gorm.Open(gsqlite.Open(":memory:"), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	t.Cleanup(func() {
+		sqlDB, _ := db.DB()
+		if sqlDB != nil {
+			_ = sqlDB.Close()
+		}
+	})
+
+	if err := db.Exec(`CREATE TABLE schema_version (version INTEGER NOT NULL DEFAULT 0)`).Error; err != nil {
+		t.Fatalf("create schema_version: %v", err)
+	}
+	if err := db.Exec(`INSERT INTO schema_version(version) VALUES(?)`, 2).Error; err != nil {
+		t.Fatalf("seed schema_version: %v", err)
+	}
+
+	originalIDRepair := ensurePostgresIDDefaultsFn
+	ensurePostgresIDDefaultsFn = func(db *gorm.DB) error {
+		return nil
+	}
+	t.Cleanup(func() {
+		ensurePostgresIDDefaultsFn = originalIDRepair
+	})
+
+	wantErr := errors.New("vite config migration failed")
+	originalMigrate := migrateViteConfigValueColumnTypeFn
+	migrateViteConfigValueColumnTypeFn = func(db *gorm.DB) error {
+		return wantErr
+	}
+	t.Cleanup(func() {
+		migrateViteConfigValueColumnTypeFn = originalMigrate
+	})
+
+	err = migrateSchema(db)
+	if !errors.Is(err, wantErr) {
+		t.Fatalf("expected error %v, got %v", wantErr, err)
+	}
+}