Migrate from Gin to Echo framework and add comprehensive integration tests

Major changes:
- Migrate all handlers from Gin to Echo framework
- Add new apperrors, echohelpers, and validator packages
- Update middleware for Echo compatibility
- Add ArchivedHandler to task categorization chain (archived tasks go to cancelled_tasks column)
- Add 6 new integration tests:
  - RecurringTaskLifecycle: NextDueDate advancement for weekly/monthly tasks
  - MultiUserSharing: Complex sharing with user removal
  - TaskStateTransitions: All state transitions and kanban column changes
  - DateBoundaryEdgeCases: Threshold boundary testing
  - CascadeOperations: Residence deletion cascade effects
  - MultiUserOperations: Shared residence collaboration
- Add single-purpose repository functions for kanban columns (GetOverdueTasks, GetDueSoonTasks, etc.)
- Fix RemoveUser route param mismatch (userId -> user_id)
- Fix determineExpectedColumn helper to correctly prioritize in_progress over overdue

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

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

internal/services/user_service.go

@@ -3,11 +3,13 @@ package services
 import (
 	"errors"
 
+	"github.com/treytartt/casera-api/internal/apperrors"
 	"github.com/treytartt/casera-api/internal/dto/responses"
 	"github.com/treytartt/casera-api/internal/repositories"
 )
 
 var (
+	// Deprecated: Use apperrors.NotFound("error.user_not_found") instead
 	ErrUserNotFound = errors.New("user not found")
 )
 
@@ -27,7 +29,7 @@ func NewUserService(userRepo *repositories.UserRepository) *UserService {
 func (s *UserService) ListUsersInSharedResidences(userID uint) ([]responses.UserSummary, error) {
 	users, err := s.userRepo.FindUsersInSharedResidences(userID)
 	if err != nil {
-		return nil, err
+		return nil, apperrors.Internal(err)
 	}
 
 	var result []responses.UserSummary
@@ -48,10 +50,10 @@ func (s *UserService) ListUsersInSharedResidences(userID uint) ([]responses.User
 func (s *UserService) GetUserIfSharedResidence(targetUserID, requestingUserID uint) (*responses.UserSummary, error) {
 	user, err := s.userRepo.FindUserIfSharedResidence(targetUserID, requestingUserID)
 	if err != nil {
-		return nil, err
+		return nil, apperrors.Internal(err)
 	}
 	if user == nil {
-		return nil, ErrUserNotFound
+		return nil, apperrors.NotFound("error.user_not_found")
 	}
 
 	return &responses.UserSummary{
@@ -67,7 +69,7 @@ func (s *UserService) GetUserIfSharedResidence(targetUserID, requestingUserID ui
 func (s *UserService) ListProfilesInSharedResidences(userID uint) ([]responses.UserProfileSummary, error) {
 	profiles, err := s.userRepo.FindProfilesInSharedResidences(userID)
 	if err != nil {
-		return nil, err
+		return nil, apperrors.Internal(err)
 	}
 
 	var result []responses.UserProfileSummary