Add generate-share-package endpoint for residence sharing

- Add POST /api/residences/:id/generate-share-package/ endpoint
- Add SharePackageResponse DTO with share code and metadata
- Add GenerateSharePackage service method to create one-time share codes
- Update JoinWithCode to deactivate share code after successful use

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

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

internal/services/residence_service.go

@@ -337,6 +337,48 @@ func (s *ResidenceService) GenerateShareCode(residenceID, userID uint, expiresIn
 	}, nil
 }
 
+// GenerateSharePackage generates a share code and returns package metadata for .casera file
+func (s *ResidenceService) GenerateSharePackage(residenceID, userID uint, expiresInHours int) (*responses.SharePackageResponse, error) {
+	// Check ownership (only owners can share residences)
+	isOwner, err := s.residenceRepo.IsOwner(residenceID, userID)
+	if err != nil {
+		return nil, err
+	}
+	if !isOwner {
+		return nil, ErrNotResidenceOwner
+	}
+
+	// Get residence details for the package
+	residence, err := s.residenceRepo.FindByID(residenceID)
+	if err != nil {
+		return nil, err
+	}
+
+	// Get the user who's sharing
+	user, err := s.userRepo.FindByID(userID)
+	if err != nil {
+		return nil, err
+	}
+
+	// Default to 24 hours if not specified
+	if expiresInHours <= 0 {
+		expiresInHours = 24
+	}
+
+	// Generate the share code
+	shareCode, err := s.residenceRepo.CreateShareCode(residenceID, userID, time.Duration(expiresInHours)*time.Hour)
+	if err != nil {
+		return nil, err
+	}
+
+	return &responses.SharePackageResponse{
+		ShareCode:     shareCode.Code,
+		ResidenceName: residence.Name,
+		SharedBy:      user.Email,
+		ExpiresAt:     shareCode.ExpiresAt,
+	}, nil
+}
+
 // JoinWithCode allows a user to join a residence using a share code
 func (s *ResidenceService) JoinWithCode(code string, userID uint) (*responses.JoinResidenceResponse, error) {
 	// Find the share code
@@ -362,6 +404,12 @@ func (s *ResidenceService) JoinWithCode(code string, userID uint) (*responses.Jo
 		return nil, err
 	}
 
+	// Mark share code as used (one-time use)
+	if err := s.residenceRepo.DeactivateShareCode(shareCode.ID); err != nil {
+		// Log the error but don't fail the join - the user has already been added
+		// The code will just be usable by others until it expires
+	}
+
 	// Get the residence with full details
 	residence, err := s.residenceRepo.FindByID(shareCode.ResidenceID)
 	if err != nil {