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/task_service_test.go

@@ -1,6 +1,7 @@
 package services
 
 import (
+	"net/http"
 	"testing"
 	"time"
 
@@ -105,7 +106,7 @@ func TestTaskService_CreateTask_AccessDenied(t *testing.T) {
 	now := time.Now().UTC()
 	_, err := service.CreateTask(req, otherUser.ID, now)
 	// When creating a task, residence access is checked first
-	assert.ErrorIs(t, err, ErrResidenceAccessDenied)
+	testutil.AssertAppError(t, err, http.StatusForbidden, "error.residence_access_denied")
 }
 
 func TestTaskService_GetTask(t *testing.T) {
@@ -138,7 +139,7 @@ func TestTaskService_GetTask_AccessDenied(t *testing.T) {
 	task := testutil.CreateTestTask(t, db, residence.ID, owner.ID, "Test Task")
 
 	_, err := service.GetTask(task.ID, otherUser.ID)
-	assert.ErrorIs(t, err, ErrTaskAccessDenied)
+	testutil.AssertAppError(t, err, http.StatusForbidden, "error.task_access_denied")
 }
 
 func TestTaskService_ListTasks(t *testing.T) {
@@ -239,7 +240,7 @@ func TestTaskService_CancelTask_AlreadyCancelled(t *testing.T) {
 	now := time.Now().UTC()
 	service.CancelTask(task.ID, user.ID, now)
 	_, err := service.CancelTask(task.ID, user.ID, now)
-	assert.ErrorIs(t, err, ErrTaskAlreadyCancelled)
+	testutil.AssertAppError(t, err, http.StatusBadRequest, "error.task_already_cancelled")
 }
 
 func TestTaskService_UncancelTask(t *testing.T) {