Add performance optimizations and database indexes

Database Indexes (migrations 006-009):
- Add case-insensitive indexes for auth lookups (email, username)
- Add composite indexes for task kanban queries
- Add indexes for notification, document, and completion queries
- Add unique index for active share codes
- Remove redundant idx_share_code_active and idx_notification_user_sent

Repository Optimizations:
- Add FindResidenceIDsByUser() lightweight method (IDs only, no preloads)
- Optimize GetResidenceUsers() with single UNION query (was 2 queries)
- Optimize kanban completion preloads to minimal columns (id, task_id, completed_at)

Service Optimizations:
- Remove Category/Priority/Frequency preloads from task queries
- Remove summary calculations from CRUD responses (client calculates)
- Use lightweight FindResidenceIDsByUser() instead of full FindByUser()

These changes reduce database load and response times for common operations.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/repositories/residence_repo.go

@@ -67,6 +67,24 @@ func (r *ResidenceRepository) FindByUser(userID uint) ([]models.Residence, error
 	return residences, nil
 }
 
+// FindResidenceIDsByUser returns just the IDs of residences a user has access to.
+// This is a lightweight alternative to FindByUser() when only IDs are needed.
+// Avoids preloading Owner, Users, PropertyType relations.
+func (r *ResidenceRepository) FindResidenceIDsByUser(userID uint) ([]uint, error) {
+	var ids []uint
+	err := r.db.Model(&models.Residence{}).
+		Where("is_active = ?", true).
+		Where("owner_id = ? OR id IN (?)",
+			userID,
+			r.db.Table("residence_residence_users").Select("residence_id").Where("user_id = ?", userID),
+		).
+		Pluck("id", &ids).Error
+	if err != nil {
+		return nil, err
+	}
+	return ids, nil
+}
+
 // FindOwnedByUser finds all residences owned by a user
 func (r *ResidenceRepository) FindOwnedByUser(userID uint) ([]models.Residence, error) {
 	var residences []models.Residence
@@ -118,42 +136,41 @@ func (r *ResidenceRepository) RemoveUser(residenceID, userID uint) error {
 	).Error
 }
 
-// GetResidenceUsers returns all users with access to a residence
+// GetResidenceUsers returns all users with access to a residence (owner + shared users).
+// Optimized: Uses a single UNION query instead of preloading full residence with relations.
 func (r *ResidenceRepository) GetResidenceUsers(residenceID uint) ([]models.User, error) {
-	residence, err := r.FindByID(residenceID)
+	var users []models.User
+	// Single query to get both owner and shared users
+	err := r.db.Raw(`
+		SELECT DISTINCT u.* FROM auth_user u
+		WHERE u.id IN (
+			SELECT owner_id FROM residence_residence WHERE id = ? AND is_active = true
+			UNION
+			SELECT user_id FROM residence_residence_users WHERE residence_id = ?
+		)
+	`, residenceID, residenceID).Scan(&users).Error
 	if err != nil {
 		return nil, err
 	}
-
-	users := make([]models.User, 0, len(residence.Users)+1)
-	users = append(users, residence.Owner)
-	users = append(users, residence.Users...)
 	return users, nil
 }
 
 // HasAccess checks if a user has access to a residence
 func (r *ResidenceRepository) HasAccess(residenceID, userID uint) (bool, error) {
 	var count int64
-
-	// Check if user is owner
-	err := r.db.Model(&models.Residence{}).
-		Where("id = ? AND owner_id = ? AND is_active = ?", residenceID, userID, true).
-		Count(&count).Error
+	// Single query using UNION to check owner OR member access
+	err := r.db.Raw(`
+		SELECT COUNT(*) FROM (
+			SELECT 1 FROM residence_residence
+			WHERE id = ? AND owner_id = ? AND is_active = true
+			UNION
+			SELECT 1 FROM residence_residence_users
+			WHERE residence_id = ? AND user_id = ?
+		) access_check
+	`, residenceID, userID, residenceID, userID).Scan(&count).Error
 	if err != nil {
 		return false, err
 	}
-	if count > 0 {
-		return true, nil
-	}
-
-	// Check if user is in shared users
-	err = r.db.Table("residence_residence_users").
-		Where("residence_id = ? AND user_id = ?", residenceID, userID).
-		Count(&count).Error
-	if err != nil {
-		return false, err
-	}
-
 	return count > 0, nil
 }