Make contractor residence optional with visibility rules

- Make residence_id nullable in contractor model
- Add created_by_id field to track contractor creator
- Update access control: personal contractors visible only to creator,
  residence contractors visible to all residence users
- Add database migration for schema changes
- Update admin panel DTOs and handlers for optional residence
- Fix test utilities for new model structure

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/repositories/contractor_repo.go

@@ -42,14 +42,28 @@ func (r *ContractorRepository) FindByResidence(residenceID uint) ([]models.Contr
 }
 
 // FindByUser finds all contractors accessible to a user
-func (r *ContractorRepository) FindByUser(residenceIDs []uint) ([]models.Contractor, error) {
+// Returns contractors that either:
+// 1. Have no residence (personal contractors) AND were created by the user
+// 2. Belong to a residence the user has access to
+func (r *ContractorRepository) FindByUser(userID uint, residenceIDs []uint) ([]models.Contractor, error) {
 	var contractors []models.Contractor
-	err := r.db.Preload("CreatedBy").
+	query := r.db.Preload("CreatedBy").
 		Preload("Specialties").
 		Preload("Residence").
-		Where("residence_id IN ? AND is_active = ?", residenceIDs, true).
-		Order("is_favorite DESC, name ASC").
-		Find(&contractors).Error
+		Where("is_active = ?", true)
+
+	if len(residenceIDs) > 0 {
+		// Personal contractors (no residence, created by user) OR residence contractors
+		query = query.Where(
+			"(residence_id IS NULL AND created_by_id = ?) OR (residence_id IN ?)",
+			userID, residenceIDs,
+		)
+	} else {
+		// Only personal contractors
+		query = query.Where("residence_id IS NULL AND created_by_id = ?", userID)
+	}
+
+	err := query.Order("is_favorite DESC, name ASC").Find(&contractors).Error
 	return contractors, err
 }